FOURTH GROUP. SEED-PLANTS. 



themselves continue in the endosperm till the food which it contains has been 

 transferred to the embryo ; occasionally they are drawn out by the elongation of the 

 stem and brought above the surface of the ground, and there unfold as the first 

 foliage-leaves. In the Coniferae they become green inside the seed in perfect 

 darkness; the formation of chlorophyll therefore takes place in this case, as in the 

 Ferns, without the co-operation of light ; it is not known whether this is the case 

 also in the Cycadeae and Gnetaceae. The young plant when set free from the seed 

 consists of an erect stem, which passes without any distinct line of demarcation into 

 the strong primary tap-root; this grows vertically downwards and sends off 

 numerous secondary roots in acropetal succession, ultimately forming in most cases 

 an extensive root-system. The young stem grows vertically upwards, and its growth 

 is usually unlimited and much more vigorous than that of all the lateral branches, 

 though there may be many of them, as in the Coniferae; in the remarkable Gnetaceous 

 species, Welwitschia, growth ceases at the apex of the stem at a very early period, 

 and there is no production even of new leafy shoots ; this is usually the case also in 

 the Cycadeae. 



There is no apical cell at the extremity of the shoots or at the points of the roots 

 in Gymnosperms; they resemble in this respect the rest of the Phanerogams, but 

 they differ from them in this that the primary meristem of the growing point of a 

 shoot either shows no differentiation, as in the Cycadeae and Abietineae, or only an 

 indistinct differentiation into dermatogen, or young epidermis, and periblem, or young 

 cortex. The well-defined axile fascicular portion (plerome-strand) is covered at the 

 apex of the root by a continuation of the cortical tissue (periblem), the layers of 

 which become thickened over the apex and split, and thus form the root-cap. 



Terminal flowers occur on the primary stem only in the Cycadeae, and not always 

 in them ; they appear in the other families on small lateral shoots, usually of a high 

 order. The flowers are always unisexual, the plants themselves monoecious or dioe- 

 cious. The male flower consists of a slender and usually much elongated axis, on 

 which the stamens, which are generally numerous, are disposed spirally or in whorls. 

 The female flowers are extremely different in outward appearance and for the most 

 part very unlike those of Angiosperms ; the Gnetaceae only have a kind of perianth 

 of more delicate leaves; there is none in the Cycadeae and Coniferae or it is 

 represented by scales. But the peculiar feature in the female flowers, apart from the 

 absence of an ovary, is the elongation of the floral axis, on which the leaves are not 

 arranged in concentric circles, as in Angiosperms, but in distinctly ascending 

 spirals, or in alternating whorls where they are numerous ; in Podocarpus and Gingko, 

 where only a few ovules are produced on a flowering axis which is either naked or 

 furnished with only small leaves, the last trace of any resemblance in habit to the 

 flowers of Angiosperms usually ceases. As our guide in this matter we have only to 

 keep to the definition, that a flower is an axis bearing sporophylls, in order to be 

 clear at all .times as to what should be called a flower in the Gymnosperms 1 . 



1 It would be well perhaps to use the expression ' flower' only in the Gnetaceae and in Angiosperms, 

 for a sporangiferous spike of Selaginella might be called a flower as much as the male inflorescence 

 of Pinus; both are in fact simply sporangiferous spikes or axes bearing sporophylls, whereas in 

 Angiosperms, at least in typical cases, further modifications occur. On the histology of the Gymno- 

 sperms see the supplementary remarks on the whole class. 



