Fungi 



195 



Satisfactory material for general laboratory purposes can be 

 secured as just described. Absolutely pure cultures can be secured 

 only by observing all the precautions necessary in bacteriological 

 work. 



Achlya is similar and equally good for illustrative purposes. 

 It is found on insects, fishes, dead fish eggs, and on algae. The 

 zoospores escape in a mass, which, for a short time, is held together by 

 a transparent pellicle; in Saprolegnia the zoospores swarm separately. 

 In Saprolegnia, the new sporangia grow up through the empty ones; 

 in Achlya, the later sporangia arise on 

 lateral branches below the earlier ones. 



Fix in chromo-acetic acid. Stain some 

 in iron-haematoxylin and some in Magdala 

 red and anilin blue, using the Venetian 

 turpentine method. For material which 

 is to be sectioned, add a little osmic acid 

 to the fixing agent. 



Albugo. This fungus is quite common 

 on Cruciferae, where the white " blisters' 1 

 or "white rust," Albugo Candida, form 

 quite conspicuous patches. Affected por- 

 tions of leaves and stems should be fixed 

 in chromo-acetic acid and cut in paraffin. 

 Sections 5 /z or less in thickness will be 

 found most satisfactory. Stain in iron- 



V 



alum and counter-stain lightly with orange 



(Fig. 51). The oosporic stage is not so 



easily recognized, but if the pods appear 



distorted it will be worth while to examine 



them. The oosporic phase of Albugo bliti is easily recognized on 



Amaranthus, where the oospores may be seen with the naked eye 



by holding the leaf up to the light. The oospores usually occur in 



more or less circular patches upon the leaf. When they occur 



among the floral structure, there is often a slight reddish coloration. 



Unfortunately for the collector, it is very seldom that any red 



coloration in Amaranthus is due to the desired material. 



FIG. 51. Albugo Candida 

 on Capsella: vertical section 

 of a blister on a leaf; prepara- 

 tion fixed in Flemming's 

 weaker solution and stained 

 in safranin, gentian-violet, 

 orange. X225. 



