66 



THE GENERAL DEVELOPMENT OF PLANTS, 



spores (97), or minute rudimentary cells, which are detached from 

 the parent plant and serve the purpose of seeds. The spores are 

 in some cases produced (probably by original cell-formation), in an 

 enlarged terminal cell, as in the Bread-Mould (Fig. 92) ; while in 

 other cases they are naked, and arise from cell-division, as in Fig. 

 93, 94. 



106. Plants of this simple structure (belonging chiefly to the 

 lower Algie and Fungi) are almost as various in form and numerous 

 in species as are the higher kinds of vegetation. Some consist of a 

 single jointed thread ; others are excessively branched ; and some- 

 times the branches are interlaced or compacted to form masses or 

 strata of considei-able size. Some of them present little or no dis- 

 tinction among the cells they consist of, each cell performing the 

 same office as any other, and each capable of producing spores or in 

 some way serving for reproduction ; such may well be regarded 

 as rows of one-celled plants, more or less united. But more com- 

 monly, even in the simplest vegetable forms, the work which the 

 plant has to perform is divided, some parts serving for vegetation or 

 nutrition, and others for reproduction, as we see is the case with the 

 Moulds, &c. Even a one-celled plant may begin to have organs, or 

 parts adapted to special purposes, as is well show^n by Botrydium 

 and Vaucheria (Fig. 85-90). As we ascend in the scale of vege- 

 table life, more and more specialization will be found at every step. 



107. A shght change in the way the cells multiply, namely, the 

 formation of partitions in two directions instead of only one, intro> 

 duces the next advance in vegetable development, giving rise to 



fe 





•I* 



97 



108. Plants of a Single Plane or Layer of Cells. Figures 18 - 22 show 



how a plant of a single spherical cell may multiply, by repeated 



FIG. 95. A piece of Delesseria Leprieurei, from Hudson River, of twice the natural size. 

 96. A portion of the wliole breadth of the same, more magnified, to show tlie cellular struc- 

 ture. The cells have thick gelatinous walls ; those in the middle are elongated, those towards 

 the margins rounded. 97. A small portion still more magnified. 



