50 WHITE RUST. 



moving water imparts to the spores of Spirogyra. In 

 order to secure certain and extensive distribution, there- 

 fore, and to provide for a succession of crops through the 

 growing season, it produces conidia or summer spores 

 in the greatest profusion, which being light and dry 

 are easily blown about by the wind, and are ready to 

 germinate at once. The thin wall and active pro- 

 toplasm of the conidia, from which they derive this 

 advantage, render them at the same time short lived, 

 so that if a conidium does not find favorable con- 

 ditions for growth within a few hours after reaching 

 maturity, it perishes. The conidia germinate in water, 

 and with best results in a film of water, such as is 

 formed by heavy dew. To still further promote dis- 

 tribution, each conidium breaks up into several active 

 zoospores, which, after moving about for fifteen min- 

 utes or so and finally coming to rest, put out a myce- 

 Hal tube that penetrates the host, and forms a new 

 plant. The zoospores, except in being colorless like 

 the parent, remind us of those of Protococcus, serving 

 the same purpose of distribution and reproduction. 



The absence of septa, except for the separation of 

 the antheridia, oogonia and conidia, making the vege- 

 tative portion a continuous cavity, is a character 

 shared with many other members of theOophyta, both 

 colorless and green forms, and with some of the molds 

 belonging to the Zygophyta. 



The student has doubtless been struck with the 

 rarity of the cases in which he could detect a fertilizing 

 tube, even where the antheridium appeared to lie in 

 the proper plane. There is doubtless a reason for this 

 aside from the mere difficulty of manipulation, which 



