700 



FUNGI 



It is by means of the zoospores and conidia that the potato 

 plants are infected, and as these are produced in countless 

 numbers, even by a single diseased plant, there is little wonder 

 that the disorder spreads with great rapidity through a crop, 

 when circumstances favour the pro- 

 duction and germination of the spores. 

 The latter are so light that their trans- 

 port from plant to plant by even gentle 

 breezes is easy ; the beating of rain 

 and planting so close that the leaves 

 of neighbouring plants touch each 



Fig. 235. — A , Conidiophore of Phylopktitora in/estans (enlarged about 200 diameters). 

 B, Single conidium or sporangium. C, Conidium germinating ; t ' germ-tube.' D, 

 sporangium setting free its zoospores z ; a zoospore at rest, later stage of 2 ; ^ zoospore 

 germinating, later stage of rt ; t germ-tube. (5, C and D, enlarged about 650 

 diameters.) 



Other, also aid in the distribution of the disease. 



While the manner of rapid reproduction and distribution of 

 the fungus and its destructive effects upon the stems and leaves 

 of the potato plant are well understood, the amount of direct 

 damage done to the tuber by Phytophthora infestans and the 

 way in which it reaches the tuber is still a matter of uncertainty. 



