PLANTS OF A SINGLE ROW OP CELLS. 69 



creeping part at the base (which spreads widely through the sub- 

 stance they live on) of long, thread-like, and usually branching 

 cells (much like those of Fig. 15), for the -most part destitute of 

 partitions ; while the upright portions are composed of a row of 

 short cells, like those of a Conferva. These are terminated in the 

 Bread-mould (Fig. 74) by a much larger cell, which developes 

 numerous and very minute rudimentary ones in its interior. In 

 Fig. 75, we have a different arrangement, namely, a cluster of 

 branches, made up of a series of bead-like, easily separable cells, 

 which are evidently formed by the process of division just illustrat- 

 ed, and which serve as seeds to reproduce the species. 



101. Spores, When the cells remain connected as they multi- 

 ply, they increase the size or complexity of the individual vegeta- 

 ble. When they separate, each becomes the initial cell of a new 

 plant. Any cell is capable of originating a new individual. No 

 sooner, however, does the plant acquire such slight complex- 

 ity as to consist even of a single series of cells, than a distinc- 

 tion begins to appear between cells adapted for vegetation, and 

 those for reproduction. Both may propagate the species : the 

 thread-like, vegetating cells which form the base of the Moulds, in 

 Fig. 75, for example, grow with the same readiness as the minute, 

 specialized cells which terminate this simple vegetation. But the 

 first appear to do so after the manner in which the higher grades 

 of plants multiply by offshoots or division of the root ; while the 

 second are analogous in this respect to the seeds or embryos of 

 such higher plants. These cells specialized for propagation, how- 

 ever they may originate, are accordingly distinguished by a special 

 name, that of SPOKES or SPORULES. We have to rise still higher 

 in the scale, however, before a well-marked distinction can be 

 drawn in all cases between cells for reproduction and cells for 

 vegetation. 



102. Conjugation, At this stage of vegetation, however, and 

 even in a large tribe of plants composed of single and simple cells, 

 a process of great physiological importance is first observed, 

 the evident equivalent of bisexuality in the higher orders, by 

 which the reproductive cells or spores are still further specialized 

 and potentiated. They are formed by conjugation ; that is, by 

 the mingling of the contents of two cells, both of which take part 

 in the formation of the resulting spore. Fig. 77-80 exhibit this 

 conjugation in a minute silicious-coated, one-celled plant, of the 



