196 THE LOWER FUNGI— PHYCOMYCETES 



P. cystosiphon (Roze & Cornu) Lindstedt in 1872, P. deharyanum 

 Hesse in 1874, and P. vexans de Bary in 1876. The economic 

 importance of the genus was first reahzed with the appearance 

 of the paper of Hesse (1874). In 1881 de Bary transferred the 

 genus to the Peronosporaceae, placed near it his own genus 

 Phytophthora, and described several additional species, P. ferax 

 de Bary, P. megalacanthum de Bary, P. intermedium de Bary, and 

 P. artotrogus (Montagne) de Bary. 



In 1892 Fischer followed de Bary in placing Pythium in the 

 Peronosporaceae, but split the genus into three subgenera, 

 Sphaerosporangium, in which the sporangia are typically more 

 or less spherical, and Aphragmium and Nematosporangium, in 

 which they are filamentous. As treated by him Nematospo- 

 rangium embraces only a single species, P. monosperrmtm, which 

 he states differs from Aphragmium in that a septum cuts off the 

 sporangium from the remainder of the hypha. In Aphragmium 

 the sporangium is indeterminate in extent, a septum being 

 lacking. 



Schroter (1893) raised Nematosporangium to the rank of a 

 genus, and extended its limits to embrace A phragmium, thus leav- 

 ing Pythium equivalent to Sphaerosporangiu7n of Fischer. More- 

 over, he created a new family, Pythiaceae, to include the two 

 genera and placed it in the Saprolegniales. In this manner, 

 Pythium and Phytophthora came to lie in different orders, the 

 latter genus being retained in the Peronosporaceae. The inclu- 

 sion of Pythium in the Saprolegniales is clearly illogical, and 

 Schroter's classification in this regard differs from those of other 

 modern authors. 



In 1907 Butler published a monographic treatment oi Pythium, 

 based on extensive research on the group in India, and presented 

 a separation of seventeen species which has stood for twenty years 

 as essentially satisfactory. Meanwhile, no other comprehensive 

 discussion of the genus has appeared. In Butler's account Nema- 

 tosporangium and Aphragmium are merged as one subgenus under 

 the latter name, his monograph covering the entire genus Pythium 

 as understood by Fischer. 



In Aphragmium the sporangium is filamentous and often 

 branched. It is e\ddently merely an indeterminate portion 

 of the mycelium functioning as a sporangium. It is not 

 separated from the remainder of the hypha by a septum, and 

 portions of the protoplasm which remains may form other 



