70 



THE GENERAL MORPHOLOGY OF THE PLANT. 



family Desmidiaceae ; where the recent dis- 

 covery of this 

 process, by Mr. 

 Ralfs, has con- 

 firmed the veg- 

 etable character 

 of these ambig- 

 uous microscop- 

 ic bodies beyond 

 all doubt. Also 

 Figure 81 shows 

 the conjugation of 

 two individuals of 



Zygnema (Spirogyra), a common plant of our 

 pools, composed of single rows of cells, near- 

 ly all of which, in the figure, are represented 

 as taking part in the conjugation. 



103. Plants of a Tissue of Cells combined in 

 one Plane, The next step in complexity is 

 seen in those Algre which consist of a few jointed tubes laterally 

 cohering with each other ; or of numerous cells united in a single 

 plane, as in the little Sea- weed, Fig. 82. This gives rise to fron- 

 dose or leaf-like forms. The name of FROND is applied to such 



expanded bodies, 

 which are neither 

 leaf nor stem, but 

 combine the ap- 

 pearance and the 

 office of both. 

 Only the simplest 

 forms, however, 



FIG. 77. Magnified individual of Closterium acutum, after Ralfs. 78. Two individuals 

 more magnified, in conjugation ; their cells opening one into the other, and the contents min- 

 gled ; in 79, condensing ; in 80, collected and formed into a spore. 



FIG. 81. Magnified view of two conjugating filaments of Zygnema, showing all the stages 

 of the process by which the cells from different approximated filaments form each a corre- 

 sponding protuberance, these come into contact, the intervening walls are absorbed, and the 

 green contents pass from one cell into the other, condense, acquire an investing membrane, 

 and so form a spore : the several stages are shown from below upwards. 



FIG. 82. A branch of Delesseria ? LePrieurei (from the Hudson River), enlarged to twice 

 the natural size. 83. A small portion more magnified, to show the cellular structure. The 

 cells have thick gelatinous walls; those in the middle are elongated, those toward the mar- 

 gins rounded. 









vm 



