950 



OF GENERATION. 



parently similar, reunite, and form but a single new cell between them. In 

 virtue of that union, a new force seems to be developed, which leads to the 

 multiplication of this first cell by repeated subdivision, until the germ-force is 

 expended, when a fresh conjugation occurs. This reunion of the cell contents 

 may take place, either by the rupture of both cells and the discharge of their 

 endochromes, around which, after their admixture, a new cell-wall is formed 

 (Fig. 236, A, 1), or by the formation of a direct communication from the interior 

 of one to that of the other; in which latter case the union of the two endo- 

 chromes may take place either in the connecting channel (A, 2), or in one of 

 the cells of the pair (A, 3), within which the sporangium is formed and matured. 

 It is in certain of the Desmideae and Zygnemata that we meet with this latter 

 type j which presents us with the first distinction between the "sperm-cell" and 

 the " germ-cell." 2. In the higher Algae, and in all the superior Cryptogamia, the 

 process is effected by the agency of moving filaments, precisely resembling the 

 spermatozoa of Animals, and developed within special " sperm-cells" in a mode 

 precisely the same with the evolution of the spermatozoa of Animals ( 959) ; 

 these appear to find their way to the germ-cells, which are sometimes developed 

 within the same receptacles, sometimes in distinct receptacles on the same plant, 

 and sometimes in different plants ; and as the result of their contact with the 

 germ-cells, the embryo originates in the interior of the latter (Fig. 236, B). 

 This embryo, in the lower Cryptogamia, is at once cast upon its own resources; 



-QttO- 



Diagram representing the three principal forms of the Generative Process in Plants : A, conjugation of inferior 

 Cryptogamia; formation of the sporangium, b, by admixture of the discharged endochromes of the parent- 

 cells, a, a. 2, production of the sporangium, 6, within a dilatation formed by the union of the two parent-cells. 

 3, production of the sporangium, 6, by the passage of the endochrome of cell a into that of cell a*, marking 

 out a sexual difference. B, fertilization of germ in higher Cryptogamia; a, sperm-cell discharging its spiral 

 filament ; a*, germ-cell, against which one of these filaments is impinging ; 6, germ produced by their con- 

 tact. C, fertilization of germ in Phanerogamia; a, sperm-cell, or pollen-grain, sending its prolonged tube 

 down the style, until it reaches a*, the germ-cell, inclosed in the ovule, the section of whose coats is shown 

 at c; from the contact of the two, is produced the germ b. 



whilst in the higher it is nourished, during its early development, by food sup- 

 plied to it by the parent. In no case, however, does the parent appear to furnish 

 that accumulation of nutritive matter for the development of the product of the 

 germ-cell, which, when included in a common envelop with it, would constitute 

 a true "seed." 3. In the Flowering Plants, the "sperm-cell" (or pollen -grain) 

 does not evolve a self-moving filament, as in the Cryptogamia; but puts forth a 

 long tube, which, insinuating itself between the soft loose tissue of the "style," 



