436 OF GENERATION AND DEVELOPMENT. 



simplest Plants, tfeese cells, as their number is successively augmented 

 by fission, are more and more widely separated from each other, and 

 may disperse themselves over an extensive surface. If, however, they 

 should remain in connexion with each other, they may form clusters, 

 or fronds (expanded leafy surfaces), according to the direction in which 

 the subdivision takes place (Fig. 133) ; and this without the slightest 

 departure from the original cellular type, which is preserved throughout 

 the structure, every part being exactly similar to every other. In these 

 composite organisms, we usually find a provision, not merely for the 

 extension of the original structure, but for the multiplication of indivi- 

 duals, which being still referable to the general type of cell-subdivision, 

 must be considered as a process of development, rather than of genera- 

 tion. This consists in the emission, from the interior of certain of the 

 cells, of broods of young cells formed in their interior ; and these, in 

 the lower aquatic plants, are very commonly furnished with cilia, by 

 the agency of which they are dispersed through the water, beginning 

 to develope themselves into the likeness of the organisms from which 

 they sprang, as soon as their movement has ceased. These " zoo- 

 spores," as they are termed, must be regarded as the representatives of 

 the gemmce or buds of higher Plants. The latter are usually developed 

 in continuity with the stock from which they originate ; but there are 

 many instances in which they are spontaneously detached ; and there 

 are few cases in which they will not continue their existence under 

 favourable circumstances, when artificially separated from it, as is 

 practised in the operations of grafting, budding, &c. 



780. The true Generative process, on the other hand, seems to con- 

 sist, throughout the Vegetable kingdom, in the reunion of the contents 

 of two cells which have been separated in the process of development 

 and multiplication, and in the production of a germ as the result of this 

 reunion, which is usually very different in its characters and properties 

 from either of the cells whose contents have contributed to form it. 

 This process has been observed to take place in the Vegetable kingdom, 

 under three principal forms, which seem to be characteristic of the 

 lowest Cryptogamia, of the higher Cryptogamia, and of the Phanero- 

 gamia, respectively. The first of these presents itself in those simple 

 Cellular Plants, in which, whether the cells remain in connexion or not, 

 their endowments are all of the same nature. At a certain time of the 

 year (it would seem) in each species, the cells approach one another in 

 pairs, and their endochromes (or coloured contents) are intermingled 

 (Fig. 134, A), either by the rupture of both cells (1), or by the formation 

 of a direct communication from the interior of one to that of the other, 

 in which case the union of the two endochromes may take place either 

 in the connecting channel (2), or in one of the pairs of cells (3). Of 

 this process, which is known as conjugation, the result is the formation 

 of a body known as a sporangium, which may be considered as the first 

 product of the true generative process ; and from this sporangium (which 

 is a single cell, or a pair or cluster of cells) a "new generation" is de- 

 veloped by the subsequent process of fission and multiplication. There 

 is here no definite distinction of the sexes, the conjugating cells being 

 apparently alike in their endowments ; such a distinction is shadowed 



