CHAPTER V. THE THALLOPHYTA. 



297 



In Fig. 495 are represented several other forms of Desmids. 



The Characeae. These are submerged fresh-water plants, 

 rooting in the muddy bottoms of ditches, ponds and sluggish 

 streams. They do not possess true roots, but fasten themselves 

 to the mud by means of root-like processes called rhizoids. 



Fig. 495. — Desmids. a, Closterium Ehrenbergii, magnified 100 diameters; b, Xan- 

 thidium fasciculatum, magnified 500 diameters; c, Micrasterias radiosa, magnified 200 

 diameters ; d, Euastrum elegans, magnified 500 diameters ; e, Cosmarium pardalis (?), 

 magnified 500 diameters ; /, Micrasterias pinnatifida, magnified about 400 diameters. 



They bear at intervals on the slender stems whorled append- 

 ages, which may be taken to represent leaves, and in the axils of 

 these, branches occur. See Fig. 496. The stem increases in 

 length by the continual division of the apical cell in a transverse 

 direction, and by the growth in length of some of the cells thus 

 produced. The cells resulting from this division are alternately 

 nodal and internodal cells. The latter become greatly elongated, 

 sometimes several inches in length, but do not again divide. 

 Not so, however, with the nodal cells. These increase but little 

 in length, but divide longitudinally to produce the lateral ap- 

 pendages, — leaves, stems and fruiting organs. From them 

 also originates the cellular cortex which in the genus Chara, but 

 not in the related genus Nitella, covers the internodal cell and 



