PYTHIUM. 289 



(5) The presence of numerous nuclei and of oil-drops 

 in the hyphae. 



(6) The gonidiophores, which are formed by the ends 

 of certain hyphae swelling up to form a gonidangium 

 which is cut off by a cross-wall or the gonidangia may 

 be intercalary and marked off by two cross-walls. 



416. Development and Germination of G-onidangium. 

 The development of the gonidangium may often be traced if 

 portions of infected seedlings are placed in water in a watch-glass 

 and examined day by day. If a piece of material showing goni- 

 dangia is placed along with a healthy Cress seedling in a watch- 

 glass of water, the germination of the gonidangia may also be 

 observed. The ends of some of the hyphae, growing out from the 

 infected seedling, swell up and become densely granular ; after 

 the formation of the cross- wall, the portion of the hypha im- 

 mediately below is seen to be partly emptied of its protoplasmic 

 contents. 



When the gonidangium germinates, it may either (1) send out 

 a protruding vesicle into which the contents pass, these dividing to 

 form numerous zoogonidia (so small that it is hard to say whether 

 they have two cilia or a single cilium) which swim about and on 

 reaching a host-plant put out a hypha to enter it ; or (2) act as 

 a gonidium and germinate directly, putting out a hypha. 



It is usually stated that the direct germination of the goni- 

 dangium, without the formation of zoogonidia, indicates partial 

 adaptation to subaerial life-conditions, but as a matter of fact this 

 type of germination occurs freely in cultures made in water. 



417. Autlieridiuxn, Oogonium, and Oospore. The 

 sexual organs should be looked for in material that has 

 already produced gonidangia, on placing it in a watch- 

 glass or a larger vessel of water. The oogonium arises as 

 a terminal (or sometimes intercalary) swelling on a hypha, 

 at first resembling a gonidangium, and is cut off by a 

 cross-wall as a spherical cell containing a single oosphere. 

 The antheridiuni arises as a lateral branch, often on the 

 same hypha a little below the oogonium, and its tip is cut 

 off by a transverse wall. 



If material is obtained, the process of fertilisation may 



be followed in a hanging drop of water (Ward's tube or 



moist-chamber slide) ; the tip of the antheridiuni comes 



into contact with the oogonium and puts out a short tube 



p. B. 19 



