490 H. MAUsn.VLL WARD. 



Hesse ^ and De Bary - both describe the formation of zoo- 

 sporangia in this species ; I have not succeeded in obtaining 

 zoospores, and can only refer to their descriptions. The 

 zoosporangium arises, according to these observers, in 

 exactly the same way as a terminal conidium, and is not to 

 be distinguished from it by outward characters, until its 

 further development. This takes place by the lateral outgrowth 

 of its wall into a kind of beak, into which the contents pass ; 

 the end then swells up quickly into a gelatinous vesicle which 

 receives the protoplasm, and this at once becomes divided up 

 into zoospores. These processes, as figured by Hesse, are 

 very similar to what occurs in Pythium proliferum, in 

 which form I have studied them very carefully ; nevertheless the 

 differences are sufficient to distinguish them. De Bary points 

 out that the conidia only produce zoospores if sown at once,* 

 and immediately on separation, in fresh water. My failure 

 to obtain the zoospores may possibly be attributed to this. 

 Besides the asexual forms of reproductive bodies, however, this 

 species possesses sexual organs of a simple and typical char- 

 ficter, and from the comparative ease and certainty with which 

 the process of fertilisation may be studied in these fungi, an 

 accurate knowledge of the essentials of the sexual process can 

 be hoped for with some success. 



In a well nourished cultivation of Pythium de Baryanum, 

 the appearance of the sexual organs usually occurs in from 

 forty- eight to sixty hours at latest, and enormous numbers 

 sometimes arise, after the crop of conidia has considerably 

 advanced. If a piece of cress-seedling, thoroughly infected 

 with the fungus, be placed in fresh water in a watch-glass or 

 open vessel, the oogonia and antheridia are commonly pro- 

 duced in a few hours : a favourable portion attached to the 

 lower side of a thin cover-slip in a suspended drop of water, 

 kept in a damp chamber — allows every step of the development 



' Loc. cit., p. 19. 

 ' ' Bot. Zeit.,' 1881, p. 523. 



^ " Zoosporen sail ich diese Conidien nach mchr als liiiclistens wenige Tage 

 langer Aufbewahrung nie bilden," 'Bot. Zeit.,' 1881, p. 52<t. 



