486 H. MARSHALL WARD. 



One great difficulty experienced by those who have 

 attempted to define the taxonomic limits of these and similar 

 organisms, comprising the Saprolegnise, &c., is to determine 

 whether they are Fungi or Alga?; but since true parasitic 

 members of the group are now known to infest land plants, as 

 well as green Algae, we may safely put this difficulty aside 

 when their want of any trace of chlorophyll or starch-forming 

 substances are also borne in mind. After all, and the opinion 

 may be abundantly supported, the exact limitation of the lower 

 Algae and Fungi is of comparatively small importance, since it 

 may be considered certain that they pass into one another at 

 one or more points. 



The name Pythium was given by Pringsheim to a group 

 of Saprolegnia-like organisms, because he found that the 

 process of formation of the "swarm-spores" differed in this 

 newly discovered type^ from that of Saprolegnia generally; 

 De Bary soon afterwards described new species of the genus,^ 

 and other observers gradually added to the list. For many 

 years, however, great confusion seems to have existed between 

 Saprolegnia, Achlya, Pythium, and other groups, and it 

 was not until a comparatively recent date that something like 

 order was arrived at. This has been accomplished by con- 

 tinuous and careful observation of the development of 

 individual forms, and much is due to the indefatigable labours 

 of De Bary, whose last monograph^ is a model for all mor- 

 phologists. 



Several of the known species of Pythium are parasitic on 

 living plants, though others appear to be habitually sapro- 

 phytes. In 1874, however, Hesse discovered a species^ which 

 seems to be ahnost omnivorous, attacking living and dead 

 plants of widely different kinds, and which can be grown on 

 animal substances as well. I shall commence by examining 

 this species in some detail, not only because it is one of the 



1 'Jalirb. f. wiss. Bot.,' B. i. 



■■^ 'Jalirb. f. wiss. liot.,' E. ii, and literature quoted below. 



» ' Beitr. z. Morph. u. PLys. der Pilze,' R. iv, 1881. 



" 'rvtliiuiu })c Bar^aiiuiii, eiu Eudoplivtibclier ScLinarolzcr,' Ilallc, 1874. 



