312 Agricultural Experiment Station, Ithaca, N. Y. 



hyplia from that on which the oogonium is borne. From the latter 

 the gonoplasm was not used. 



Tliese oospores or fertilized eggs mark a very important phase in 

 the life history of the fungus. They will eventually germinate 

 and produce the mycehum again, which under favorable conditions 

 will start the disease anew. But the remarkable thing about the 

 oospores is that they can not germinate immediately, except in rare 

 instances, but must undergo a long period of rest, and hence are 

 sometimes termed resting spores. In this condition they are 

 capable of resisting degrees of cold and dryness which would prove 

 fatal to the vegetative portion of the fungus. This accounts partly 

 for the appearance of the disease after long periods of drought and 

 after the inclement weather of the winter season in some sections. 



Not only does the thicker wall of the oospore offer greater pro- 

 tection against an unfavorable environment, but the protoplasm 

 undergoes a marked change before it finally enters upon this 

 enforced period of rest. This change is practically a metamorphosis, 

 the complete nature of which we do not understand. Among other 

 changes there is probably a change in the molecular or physical 

 structure of the j^rotoplasm by which a large amount of a fatty 

 substance is separated and forms a very large globule and sometimes 

 other smaller ones which occupy a large part of the space of the 

 oospore. The protoplasm thus becomes transformed into a state 

 highly resistant to outside conditions and incapable of growth for a 

 long period, even though the environment may be most favorable 

 for growth. The period of rest lasts for several, four to five, months. 

 They will resist freezing for weeks, followed by drying, without injury^ 



Propagative Organs. — Organs of another kind than oogonia and 

 antheridia are developed on the mycelium. The function of these 

 is chiefly for the immediate and rapid propagation of the numbera 

 of the parasite. The organs are like the oogonia, either terminal 

 or intercalary swellings of the hyphae, and at first do not differ 

 materially from them before the defferentiation of the egg cell 

 and antheridium. These organs are exactly alike in form but differ 

 in the discharge of their functions and are termed respectively, 

 conidia, resting conidia, and zoosporangia. 



Conidia. — The conidia measure about the same as the oogonia 

 and when fresh water is added to them they will germinate im- 

 mediately after maturity, which is attained upon reaching their 

 full size. 



