MICROSPH^ERA ALNI OR M. QUERCINA. 73 



be largely produced without the transfer of protoplasm 

 from the antheridium to the carpogonium, which con- 

 stitutes fertilization. On this account some other plants 

 better illustrate the fertilization and the early growth of 

 the "fruits" than the one used. Coleoch&te, already 

 studied in connection with Chlorophyceae, and Nemalion 

 and Batrachospermum among the red Algae illustrate 

 the same general process. 



The comparison of Micros phara with Albugo is very 

 instructive in showing how the same conditions have 

 been reached by widely different plants. Both are 

 parasitic, the one living within the host, and the other 

 upon its surface, both deriving nourishment by means 

 of haustoria, in addition to what is absorbed directly 

 through the walls of the filaments. 1 Both bear aerial 

 spores, which are formed by successive abstrictions 

 from vertical mycelial threads, the main difference being 

 that in Albugo these must break through the surface- 

 tissue of the host, and are therefore required to grow 

 in groups in order to exert the necessary force, while 

 in the superficial Microsph&ra they are single and evenly 

 distributed. The conidiospores of Albugo sometimes 

 germinate by formation of zoospores and sometimes 

 by direct formation of a filament, while those of Micro- 

 sphcera grow into a mycelial filament at once, a differ- 

 ence whose cause is not known. Both plants form rest- 

 ing spores, but in Albugo the protective covering is the 

 thickened wall of the spore; in Micros phar a it is a 



1 To see how some of the parasites that are closely related to Micro- 

 sphczra obtain their food consult the drawings and text of an article by 

 Grant Smith on "The Haustoria of Erysipheae." Bot. Gaz. 29 : 153-184. 



