66 PLANT-LIFE 



tion. Details of Vaucheria sessilis are admirably illus- 

 trated in Plate IL, Figs. 4-7. This plant, in common with 

 others of its kind, is extremely simple in its vegetative 

 parts. The thallus consists of an irregularly branched, 

 tubular green filament, the cell-wall being of cellulose, 

 and the protoplasm, with which it is lined interiorly, 

 includes countless nuclei and chloroplasts. The fila- 

 ment is attached to a substratum by a branched, 

 colourless, root process. The filaments are visible to 

 the naked eye; they form a sort of loose green felt on 

 moist soil, and not infrequently occur on the soil of 

 plant-pots in greenhouses. Species of Vaucheria also 

 grow in salt and fresh water. The growth of the fila- 

 ments is apical, and the protoplasm at the growing 

 points of the stem and branches is always colourless. 



Asexual reproduction by zoospores takes place mostly 

 in water, or when the conditions are very moist. The 

 zoospore is formed, at the end of a branch, from a portion 

 'of the protoplasm, which accumulates there and becomes 

 dense. The cell-wall at this point bulges into a club- 

 like form, and that portion becomes divided from the 

 branch by the growth of a septum. Thus, a separate 

 cell is formed; it is dignified by the term " zoospor- 

 angium." Only one zoospore is formed in this cell, but 

 it is notable for possessing many nuclei and chloroplasts. 

 The zoospore eventually escapes from the apex of the 

 ceU through a narrow opening. As the opening is 

 narrower than the bulk of the zoospore, the latter is 

 compelled to change its form as it forces its way through. 

 Sometimes it breaks into two portions in the effort to 

 escape, in which event each portion becomes a zoospore. 

 The zoospores usually emerge in the morning. They 



