VAUCHERIA SESSILIS. 49 



ANNOTATIONS. 



We have in Vaucheria a green Alga which is, in some 

 ways, quite peculiar. It has a ccenocytic plant body; 

 it is relatively rather large, and produces massive zoospores 

 which are covered with cilia and are of immense size 

 when compared with other zoospores. These are called 

 compound zoospores, and are supposed to represent many 

 small zoospores, each pair of cilia protruding through a 

 thin peripheral sheath corresponding to the pair of a 

 simple zoospore. Furthermore, the plants of this genus 

 have a distinct tendency to frequent damp earth rather 

 than to live in the water. 



As a form illustrating the line of evolution of sexual 

 reproduction in the Algae Vaucheria is quite significant. 

 Here the gametes are not similar, as in Ulothrix and 

 Spirogyra, one having become large and inactive, while 

 the other is small and active. This differentiation is 

 indicated by using the term female gamete, or egg, for 

 the larger gamete, and male gamete, or sperm or anther o- 

 zoid, for the smaller one. The larger size of the oospore, 

 produced by union of the sperm with the egg, makes 

 possible the storage of greater amounts of food material 

 for the nourishment of the new plant when it germinates. 

 Fertilization is accomplished by the active swimming 

 of the sperm to the egg and fusing with it. Since the 

 number of sperms is very much greater than the number 

 of eggs, the chances of fertilization are thereby greatly 

 increased. 



It is to be noted further that ordinary vegetative cells 

 do not produce either zoospores or gametes. In the 



