,'500 PHANEROGAMS. 



formation of chlorophyll taking place, as in Ferns, without the assistance of light. 

 It is not known whether the same thing occurs also in the Cycadeae and Gnetaceae. 

 The young plant, freed from the seed, consists of an erect stem, passing below 

 insensibly into the vertically descending tap-root, from which numerous secondary 

 roots soon proceed in acropetal order, usually forming finally a well-developed 

 root-system. The embryonal stem grows vertically upwards, and is usually not only 

 unlimited in its growth, but is much stouter than all the lateral shoots, even when 

 these are formed in abundance, as is the case with Coniferae. In the remarkable 

 Gnetaceous Wehvilschta, however, the apical growth altogether ceases at a very early 

 period, and even the production of new leafy shoots is suppressed, as is usually the 

 case also in Cycadeae. 



An apical cell does not exist either at the ends of the shoots or at the apices of 

 the roots of Gymnosperms. In this respect they resemble the other Phanerogams, 

 but they differ from them in that the primary meristem of the Punctuni vegetaiionis of 

 the stem shows either no differentiation (Cycadeae, Abietineae), or only an indistinct 

 differentiation, of Dermatogen (young epidermis) and Periblem (young cortex). At 

 the apex of the root the well-defined axial fibro-vascular mass (Plerome) is covered by 

 a continuation of the cortical tissue (Periblem). Layers of cells belonging to this 

 tissue, which cover the apex, become thickened and split off, thus forming the root- 

 cap. The root-cap therefore is not derived here, as in most Angiosperms, from the 

 active growth and splitting of the young epidermis (Dermatogen), or from a proper 

 meristematic layer (Calyptrogen). 



The Flowers are usually developed on small lateral shoots, often of a high order 

 of ramification ; terminal flowers occur on the primary stem only in the Cycadeae 

 (and in them not exclusively). They are always diclinous; the plants themselves 

 monoecious or dioecious. The male flower consists of a slender axis usually greatly 

 elongated, on which the staminal leaves are arranged in large numbers usually 

 spirally or in whorls. The female flowers are remarkably different in their external 

 appearance, and usually very unlike those of Angiosperms. A kind of perianth of 

 rather delicate leaves occurs only in Gnetaceae ; in Coniferae and Cycadeae it is 

 wanting or is replaced by scales. But what makes the female flowers peculiarly 

 strange, independently of the absence of an ovary, is the elongation of the floral 

 axis, on which the foliar structures are placed not in concentric circles as in Angio- 

 sperms, but in a distinctly ascending spiral arrangement, or in alternating whorls 

 when they are numerous. When only a few ovules are produced on a naked 

 or small-leaved inflorescence, as in Podocarpus and Salisburi'a, the last trace of 

 resemblance in habit to the flowers of Angiosperms ceases. But to clearly under- 

 stand the matter it is only necessary to retain distinctly in mind the definition of 

 a flower, viz. an axis bearing members which are modified for the production of 

 spores. 



On the histology of the Gymnosperms see the remarks at the conclusion of the 

 description of the whole class. 



