284 



PART IV. VEGETABLE TAXONOMY. 



The plants multiply in several different ways. When the 

 ponds in which they grow begin to dry up, the protoplasm 

 descends into the rhizoids and there breaks up to form numerous 

 rounded cells which are capable of enduring desiccation. When 

 favorable conditions return, these either germinate and form new 

 plants or immediately develop into sporangia. 



The upper or bulbous part of the plant, when mature, also 

 becomes a sporangium. The spores discharged by this may be 

 of two kinds ; one kind has but one cilium, and after moving 

 about for a while it comes to rest and develops immediately into 

 a new plant ; the other possesses two cilia and conjugates with 

 another similar spore forming a zygospore, and this, sooner or 

 later, develops into a new plant. The figure shows the plant in 

 the act of discharging its zoospores. 



a b 



Fig. 480. — Portions of fertile filaments of Vaucheria sessilis, showing mode of sexual 

 reproduction, a, a, a, a, oogonia ; b, b, b, antheridia ; c, oospore ; d, e, germinating 

 oospores; f, antherozoids. Magnified about 175 diameters. 



The Vaucherias, or Green Felts, form another group of the 

 Coeloblasteae. They occur as dense, felt-like masses in wet soil, 

 on dripping rocks adjacent to springs, and in other similar 

 situations. 



The individual filaments in some species attain a length of 

 eight or ten inches. They root in the mud by means of rhizoids 

 similar to those of Botrydium, and the filaments are more or 

 less branching. Besides chlorophyll-bodies, they contain numer- 

 ous oil-globules distributed through the interior of the tubes. 



