OBSERVATIONS ON THE GENUS PYTHIUM. 611 



'L\\ • Within the cells of a large species of Spirogyra, observed (j^'^*^^ 

 this summer (1882), I found the Pythiura with very delicate 

 hyphae figured in fig. 37. It was not pi-esent in any consider- 

 able quantity, and all attempts to cultivate it in the mass 

 failed, as did also my endeavours to make it spread to other 

 Algae or cress-seedlings. I was also unsuccessful in the search 

 for zoospores and sporangia, and am thus unable to state 

 exactly what species it was. It is an obvious suggestion that 

 this was probably the earlier Pythium gracile of Schenk, 

 which was discovered in similar algal cells, and of which the 

 sexual organs are not known. If this be the case, it is clear 

 that De Bary's P. gracile is a diflferent species, and this would 

 be in accordance with his failure to cultivate that form on 

 living Algae — it being, so far as is known, a saprophyte only.^ 

 It may be considered probable, from the evidence at disposal, 

 that the form here discovered is really Schenk's P. gracile 

 (De Bary's P. reptans); and, at any rate, it were better to 

 assume this for the present than to assign a new name to my 

 Pythium until further observations are to hand. 



The hyphse of this species are very slender much branched 

 filaments, which bore through the septa and side walls of the 

 Spirogyra in all directions, causing the chlorophyll bands to 

 become contracted into irregular lumps and bands, which 

 retain their green colour however for a long time before they 

 slowly decay. The great interest attaching to the specimens 

 observed was, that oogonia with oospheres and antheridia 

 were produced in the normal course of the cultivation, and it 

 is clear that the oospheres and oospores differed consider- 

 ably from those of P. gracile (De Bary), in that the ripe 

 oospore is much smaller than the oogonium, whereas in 

 De Bary's P. gracile the oospore entirely fills the cavity of 

 the oogonium ; the antheridial cell is also shorter and broader. 

 The fertilising process was observed and offers nothing specially 

 worthy of note differing from what has been described. In 

 fig. 39 the very short anther id ium, at the end of a very 



' 'Bot. Zeit.,' Sept., 1881, p. 572. 



