Part 44

Dammara-resin, which is used for varnish, is obtained from Agathis (Dammara) species (New Zealand, Philippine Islands).

Order 2. =Abietaceæ (Pine and Fir Trees).= The leaves are spirally arranged and needle-like. The flowers are monœcious. The male flowers are long, and catkin-like, with numerous stamens, each bearing two oblong pollen-sacs. The pollen-grains are most frequently tri-lobed, having two bladder-like appendages, formed as outgrowths of the exospore, to assist in their distribution by the wind (Fig. 267 N). The bracts are arranged spirally. The union between the bract and the ovuliferous scale, which is found in the preceding order, is not in this instance so complete; these scales make their appearance as two free parts, and are attached only at their bases (Fig. 268); the lower portion, that is the cover-scale, in most instances remains quite small (Fir, Red Pine, and others), it is only in the “Noble Pine” (Abies) and Pseudotsuga douglasii, that it attains a greater length than the ovuliferous scale (Fig. 267, B-G). On the other hand the upper part, the ovuliferous scale (the vascular bundles of which have the bast turned upwards), grows strongly and elongates, especially after fertilisation, becoming woody or leathery; it is commonly termed the “cone-scale,” but is in reality only homologous with a part of the “cone-scale” in the other order of Pinoideæ. On the side of the ovuliferous scale, turned towards the axis, are situated two ovules with micropyles directed inwards. The seeds are most frequently provided with a false wing (a tissue-like part of the surface of the ovuliferous scale). Cotyledons, more than 2, verticillate. Fertilisation does not take place until some time after pollination. In Pinus, for instance, the pollen-tube only penetrates the nucellus for a short distance during the year of pollination, and then ceases its further growth, fertilisation not taking place until after the middle of the next year; whilst the seeds ripen about a year and a half after pollination. In the Larch and others, the seeds are mature in the autumn succeeding pollination.

Abies (Fir). The leaves are often (e.g. Ab. pectinata) displaced into 2 rows, flat and indented at the apex, with 2 white (wax-covered) lines on the under surface, in which the stomata are situated. The leaf-scars are nearly circular and do not project. The cones are erect. The cover-scales and the ovuliferous scales separate from the axis, to which they remain attached in other genera.--~Tsuga has leaves like Abies, but by the slightly projecting leaf-scars, and cones with persistent scales, it forms the transition to Picea.--Pseudotsuga has leaves similar to those of Abies and persistent carpels as in Picea, but the cover-scales grow as in Abies and project beyond the ovuliferous scales (P. douglasii, Fig. 267). These two genera are considered as sub-genera of Abies.~--Picea. The leaves project on all sides, square and pointed; the leaf-scars are rhombic, on projecting leaf-cushions. The cones are pendulous. The cover-scales are much shorter than the leathery, persisting ovuliferous scales.--The genus Larix (Larch) differs from all the others in having deciduous leaves (the three preceding have leaves which persist for eleven to twelve years). It has long-branches with linear foliage-leaves and short, thick, perennial dwarf-branches, which each year form a new rosette of foliage-leaves, similar to those on the long-branches. The male flowers and the erect cones resemble those of Picea, and are borne on dwarf-branches.--Cedrus (Cedar) resembles Larix to some extent, but has persistent leaves (C. libani, C. deodara).--Pinus (Pine) has long-branches and dwarf-branches. The leaves of the long-branches are scale-like and not green; the dwarf-branches have very limited growth, and persist for three years; they arise in the axils of the scales borne on the long-branches of the self-same year, and each bears 2–5 foliage-leaves, they are also surrounded at the base by a number of membranous bud-scales. The cone-scales have a thick, rhomboid extremity (the “shield”).

The buds which develope into long-branches arise at the apex of other long-branches, and being very close together, form false whorls. The female cones occupy the position of long-branches, and take about two years for their development. The male flowers arise close together, and form a spike-like inflorescence at the base of a long-branch of the same year. The male flowers occupy the position of dwarf-branches, so that a female cone may be considered to be a modified long-branch, and a male cone a modified dwarf-branch. The main axis of the seedling has needle-like leaves, similar to those found on the older parts, and on dwarf-branches; it is not until some time later that the dwarf-branches are developed and the permanent arrangement attained.

USES. Several species are commonly cultivated in this country, partly on heaths and moors, and partly in plantations and as ornamental trees, such as Mountain Pine (Pinus montana, Cen. Eur.); Austrian Pine (P. laricio, Eur.); Scotch Fir (P. silvestris, Eur.); Weymouth Pine (P. strobus, N. Am.); common Red Pine (Picea excelsa, Cen. and N. Eur.); White Pine (P. alba, N. Am.); Abies pectinata (Common Fir, S. and Cen. Eur); A. nordmanniana (Crimea, Caucasus); A. balsamea (N. Am.); Tsuga canadensis (N. Am.); Pseudotsuga douglasii (N.W. Am.); Larch (Larix europæa, Alps, Carpathians); L. sibirica (N.E. Russia, Siberia).--The wood of many species, especially Pine, on account of its lightness and because it is so easily worked, is very well adapted for many useful purposes. The wood of the Yew-tree is very hard and is used for ornamental turning. Resin and Turpentine (i.e. Resin with essential oils, the name being derived from the Terebinth-tree, from which formerly a similar material was obtained) are extracted from Pinus laricio and P. pinaster. Oil of Turpentine is obtained by distillation of turpentine with water; Tar by dry distillation of Pine-wood. Canada-balsam is from North American Abies-species (A. balsamea and Fraseri). The officinal Turpentine is mainly obtained from Pinus pinaster (South of France), P. tæda, australis, strobus (Weymouth Pine) and other North American species; more recently also from P. silvestris (Scotch Fir), maritima, laricio, Picea excelsa, and others; Venetian Turpentine, from Larch (S. Eur.) Amber is resin from a Tertiary plant (Pityoxylon succiniferum), closely related to the Pine, which grew especially in the countries round the South-East coast of the Baltic. Pinus pinea (the Pine, S. Eur.) has edible seeds and also P. cembra (in Cen. Eur. and Siberia).

Order 3. =Taxodiaceæ.= The vegetative leaves and cone-scales are arranged spirally. The ovules (2–9) are situated either at the base of the ovuliferous scales, in which case they are erect; or at their centre, when they are generally more or less inverted. The ovuliferous scale is more or less united with the cover-scale, and projects beyond the surface of the cone-scale, like a comb (Fig. 269). The vascular bundles, which extend into the cover-scale, have the usual leaf-arrangement, viz. the wood placed above the bast; while those bundles which enter the ovuliferous scale have this arrangement of the bundles reversed.

Taxodium distichum (the North American “Swamp Cypress”) has annual dwarf-branches, with distichous leaves, and cone-like “pneumathodia.” In the Tertiary period it was very common in the Polar regions. Sequoia (Wellingtonia) gigantea is the famous Californian Giant-Fir, or Mammoth-Tree, which attains a height of 300 feet, a diameter of 36 feet, and is said to live for 1,500 years. Cryptomeria japonica (Japan, China) has the least adnate ovuliferous scales; Glyptostrobus (China); Arthrotaxis (Tasmania); Sciadopitys verticillata (the only species in Japan) has, like Pinus, scale-like leaves on the long-branches, of which those which are situated at the apex of the annual shoots support “double needles,” i.e. dwarf-branches similar to the two-leaved dwarf-branches in Pinus, but without bud-scales, and with the two leaves fused together at the edges into one needle, which turns its upper surface away from the long-branch.

Order 4. =Cupressaceæ= (=Cypresses=). The leaves are opposite or verticillate, sometimes acicular, but most frequently scale-like (Fig. 270). In the species with scale-like leaves, the seedlings often commence with acicular leaves (Fig. 272), and branches are sometimes found on the older plants which revert to this form, seeming to indicate that the acicular leaf was the original form (atavism). The so-called “Retinospora” species are seedling-forms of Biota, Thuja, Chamæcyparis, which have been propagated by cuttings, and retain the seedling-form. The flowers are monœcious or diœcious. The male flowers are short, and have shield-like stamens, bearing most frequently several pollen-sacs. The cover-scales and ovuliferous scales are entirely fused together and form undivided cone-scales, opposite or whorled; the ovuliferous scales have slight projections near the base on which 1–2–several erect ovules are developed (Fig. 274). Most frequently 2 cotyledons.--Evergreen trees and shrubs.

Juniperus (Juniper). Diœcious. The cone-scales become fleshy and fuse together to form most frequently a 1–3 seeded “berry-cone.” ~J. communis (Common Juniper) has acicular leaves, borne in whorls of three, and the “berry-cone” is formed by a trimerous whorl of cone-scales (Fig. 273). J. sabina and J. virginiana have “berry-cones” formed from several dimerous whorls of cone-scales; the leaves are connate and opposite, needle-and scale-like leaves are found on the same plant.~

Cupressus (Cypress). Monœcious. The cones are spherical; the cone-scales shield-like, generally five-cornered and woody (Fig. 270), each having many seeds. The leaves are scale-like.--Thuja. Monœcious. Cones oblong. The cone-scales are dry, as in the Cypress, but leathery and imbricate, and not shield-like; each cone-scale bears 2–3 seeds. The leaves are most frequently dimorphic; those leaves which are situated on the edges of the flat branches are compressed, and only these bear buds, which are developed with great regularity, generally alternately, on both sides of the branch; those which are situated on the flattened surfaces are pressed flat and broad, and never bear branches (Fig. 271). Along the central line of each leaf there is a resin-canal (Fig. 271).--~Chamæcyparis, Callitris, Libocedrus, Thujopsis (1 species: T. dolabrata; in Japan).~

OFFICINAL. Juniperus sabina from Central and South of Europe (the young branches yield an essential oil). The wood of J. communis is used in the production of an essential oil, and J. oxycedrus in the production of empyreumatic oil. The “berry-cone” of J. communis is officinal, and is also used for gin.--The wood of J. virginiana (N. Am.) is known as red cedar, and is used for lead-pencils. Sandarack resin is obtained from Callitris quadrivalvis (N.W. Africa).

THE FOLLOWING ARE CULTIVATED IN GARDENS:--Thuja occidentalis (Arbor vitæ) (N. Am.), and orientalis (China, Japan); Juniperus sabina and virginiana; Thujopsis dolabrata (Japan); Cupressus lawsoniana (California), C. sempervirens (S. Eur., W. Asia), and other species, are grown especially in conservatories, and in Southern Europe particularly in cemeteries.--The Retinospora species which are so often planted, do not belong to an independent genus, but are obtained from cuttings, taken from seedling-plants with acicular leaves (see page 267).

Class III. =Gneteæ.=

This class, independent of extinct forms, comprises the most highly developed of the Gymnosperms, partly from the circumstance that a perianth of 2–4 members encloses the terminally placed ovule, which is provided with one, or (in Gnetum) two, integuments, and partly owing to the fact that the wood has true vessels. There is only one order.

Order. =Gnetaceæ.= The three known genera differ very much in appearance. Welwitschia mirabilis (from the deserts of South Western Africa) is the oldest (?) genus now living. It resembles a giant radish, in that the hypocotyl is the only part of the main axis of the stem which becomes developed. It attains a circumference of upwards of four metres with a length of 1/2½-⅔ of a metre. It bears only two oblong, leathery leaves (Fig. 275) which are torn into segments at the apex and lie on the surface of the soil; these are the two first foliage-leaves which succeed the cotyledons, and they are remarkable for their enormous length (upwards of two metres) as well as for their long duration, living as long as the plant itself. In their axils are situated the 4-rowed, spike-like male and scarlet-coloured female cones, upon dichotomous branches. The perianth consists in the ♂ of 2 alternating pairs of leaves, the inner ones of which are slightly united. The andrœcium likewise consists of 2 whorls: the external (transverse) with 2, the internal with 4 stamens; the lower halves of the 6 filaments uniting to form a cup. Each of the terminal anthers corresponds to a sorus of 3 sporangia, the sporangia being fused together, and opening at the top by one three-rayed cleft. In the centre of the ♂-flower there is a sterile ovule. In the ♀-flower a perianth of two connate leaves is present.--Ephedra (desert plants, especially in the Mediterranean and W. Asia) at first sight resembles an Equisetum; the stems are thin, long-jointed, and the leaves opposite, small, and united into a bidentate sheath; ♂-perianth of two connate leaves (median leaves); 2–8 stamens united into a column. Each anther is formed of 2 sporangia (is bilocular). ♀ mainly, as in Welwitschia. The seeds are surrounded by the perianth which finally becomes red and fleshy. There are 30 species.--Gnetum has opposite, lanceolate, pinnately-veined, leathery leaves. They are mostly climbers (Lianas) from Tropical Asia and America. The ♂-flowers have a tubular perianth, (formed from two median leaves) which surrounds a centrally-placed filament, bearing 2 anthers. In the ♀-flower there is a similar perianth, surrounding an ovule provided with 2 integuments. The perianth becomes fleshy and envelops the hard seed. 20 species.

From the circumstance of Welwitschia having ♂ flowers which, besides stamens, possess also a rudiment of an ovule, Celakovsky draws the inference that the earliest Gymnosperms had hermaphrodite flowers which from this structure became differentiated entirely into ♂-and ♀-flowers, with the exception of Welwitschia only, in which this differentiation was only carried out in the ♀-flower. This theory has so far been scarcely proved.

=Fossil Gymnosperms.=

The earliest continental plants which are known belong to the CORDAITACEÆ, a group of plants which existed as early as the Silurian period; they were Gymnosperms, but it has not yet been determined whether they were Cycads or Conifers. The CYCADS, even in the Coal period, were scarce; they attained their fullest development in Jurassic and Cretaceous periods, during which they were rich in species and genera, and extended as far as the Polar regions. In addition to these, Taxaceæ, Abietaceæ, and Taxodiaceæ appeared in the Carboniferous period. The TAXACEÆ appear to have attained their culmination in the Jurassic and Cretaceous periods; Ginkgo appears in the Rhætic; Torreya, in the Cretaceous; Taxus and Podocarpus in the Tertiary periods. The ABIETACEÆ also appear in the Carboniferous; Pinus was first known with certainty in the English Weald and in the Cretaceous; almost all other contemporary genera are represented in this latter period. The ARAUCARIACEÆ first appear, with certainty, in the Jurassic. The TAXODIACEÆ may be traced back as far as the Carboniferous (?); Sequoia is first found in the lowest Cretaceous, at that period it spread throughout the entire Arctic zone, and being represented by a large number of species, formed an essential part of the forest vegetation. Sequoia played a similar part in the Tertiary period. The CUPRESSACEÆ are first known with certainty in the Jurassic, but they appeared more frequently and numerously in the Tertiary period, in which most of the present living genera were to be found. The GNETACEÆ, according to a theory advanced by Renault were represented in the Coal period by the genus Stephanospermum, which had four ovules enclosed by an envelope.

DIVISION V.

ANGIOSPERMÆ.

See pages 3 and 224. To this Division belong the majority of the Flowering-plants. They are divided into two parallel classes, the Monocotyledons and the Dicotyledons, which differ from each other not only in the number of cotyledons, which, with a few exceptions, is one in the former, two in the latter, but also in the internal structure of the stem, the venation of the leaves, the number of the parts of the flower, etc. ~Assuming that these two classes have sprang from a common origin, it is amongst the Helobieæ in the first, and amongst the Polycarpicæ in the second class that we might expect to find closely allied forms, which might reasonably be supposed to have varied less from this original type. As for the rest, they seem to stand quite parallel, without exhibiting any close relationship. It is scarcely proved that the Monocotyledons are the older class.~

According to this view the principal divisions of the Angiosperms would be represented thus:--

=Angiospermæ.=

Sub-division. Sub-division. CHALAZOGAMES. POROGAMES.

Class. Classes. Chalazogames. Monocotyledones, Dicotyledones.

More recently Nawaschin (Bull. Acad. Imp. Sci. St. Petersb., ser. iii., xxxv.) has shown that Betula, and Miss Benson (Trans. Linn. Soc., 1894) that Alnus, Corylus, and Carpinus also belong to the Chalazogams.

Our knowledge, however, is still so incomplete that one would hesitate to accord the full systematic value which Dr. Treub attaches to his discovery until the limits of the Chalazogamic group are better defined; and it would hardly be justifiable to include the Casuarinas and the above-noted genera in one family.]

Class 1. =Monocotyledones.=