2 9 8 



PART IV. VEGETABLE TAXONOMY. 



keeps pace with its growth. In this mode of growth, as well as 



in the structure of their fruiting 



organs, the Characese are peculiar 



among plants. In complexity of 



structure, also, they rank highest 



among Algae. The plants are 



abundant in species, and are 



widely distributed over the world, 



but they all belong to the two 



genera already mentioned. Some 



are of small size, only one or two 



inches high ; other species attain 



the height of two or three feet. 



Nearly all are gregarious in their 



habits. 



They agree with the Conjuga- 

 te in not producing swarm-spores, 

 their asexual reproduction being 

 by means of tuber-like structures 

 borne on the subterranean parts, 

 or by peculiar branches which 

 form rhizoids on their basal nodes 

 and become separated from the 

 parent plant. 



They reproduce sexually by 

 means of oogonia and antheridia, 

 both of which have interesting 

 peculiarities in their structure. 

 These organs are, in some species, 

 both borne on the same plant ; 

 in others, on different individuals ; 

 they occur at the nodes, and may 

 be regarded as modified leaves. 

 The oogonium is at first a single 

 cell, but in the course of its de- 

 velopment it divides transversely, 

 and the apical cell becomes en- 

 larged and develops into a germ- 

 cell. This soon becomes covered by a layer of cells growing up 





Fig. 496. — Portion of Chara plant, about 

 natural size, showing arrangement of 

 leaves and branches. 



