254 



PART III. THE CLASSIFICATION OF PLANTS. 



mucilaginous cell-wall, and, entering the oosphere at the receptive spot, ferti- 

 lises it. 



After fertilisation, the oosphere becomes an oospore, surrounding itself with 

 a proper wall. The more internal walls of the investing filaments become 

 thickened, and assume a dark brown colour. The whole organ falls off and 

 undergoes a period of quiescence. 



On germination, a planoconvex mass of clear protoplasm collects at the apical 

 end of the oospore, the starch -granules being aggregated in the posterior part 

 of the oospore ; a transverse wall is then formed, separating these two parts 

 from each other. The smaller cell then divides into two by a wall at right angles 

 to the first, and from these two cells the embryo is developed. The hard invest- 

 ment of the oospore is ruptured at the apex, and the two cells grow out as fila- 

 ments, the upper forming the shoot, the lower the root, of the embryo (Fig. 182). 

 The root-cell may at once elongate into a colourless multicellular filamentous 



root, or it may divide so as to form 

 a primary root and two lateral roots. 

 The shoot-cell, which contains chloro- 

 plastids, undergoes transverse divi- 

 sion to form a filament consisting of 

 a small number of cells. The lowest 

 cell, as well as the upper cells, un- 

 dergo no further division but simply 

 elongate. The cell next above the 

 lowest cell, the intermediate cell, is 

 divided by two transverse walls 

 forming a short cell at each end with 

 a long cylindrical cell between them ; 

 each of these short cells undergoes 

 division to form a node, whilst the 

 long cell remains undivided and con- 

 stitutes an internode. The peri- 

 pheral cells of the lower node grow 

 out into adventitious roots; those of 

 the upper node give rise to leaves, 

 forming the only whorl of the em- 

 bryo, except one cell which becomes the apical cell of the stem of the adult 

 plant, and, by its growth and division, gives rise to it (Fig. 183). 



The einbryogeny of the Characeoe is in the first place meroblastic (see p. 13), 

 that is, the embryo is developed from a part only of the oospore. The larger 

 posterior part of the oospore takes no share in the formation of the embryo, but 

 serves to supply the embryo with the nutrient material necessary for the earlier 

 stages of its development. Moreover it is heteroblastic, an embryonic form inter- 

 vening between the oospore and the adult. The life-history presents no alter- 

 nation of generations. 



Parthenogenesis has been observed in Chara crinita ; the oosphere of this 

 plant germinates without fertilisation. 



The Characeoe are extensively propagated in a vegetative manner. The roots 

 sometimes develope into small spherical unicellular bulbils filled with starch : 



FIG. 182. Meroblastic development of the 

 embryo from the oospore of Tolypella intri- 

 cata ( x 00 : after De Bary) ; s embryonic 

 shoot ; r embryonic root. 





