WHITE RUSTS. 135 



five plants whicli had not received the water 

 impregnated with zoospores upon their cotyledons 

 vegetated without any indications of the parasite. 

 Amongst the eighteen plants which were inoculated 

 by watering the cotyledons, four only were not 

 attacked by the parasite, fourteen bore the " white 

 rust.^^ In six of these it did not extend beyond 

 the cotyledons ; in the others it also appeared on 

 the stems and leaves. 



From these experiments it may be deduced that 

 plants are not infected by spores of the parasite 

 entering at the roots, or by their leaves, but that 

 inoculation takes place through the medium of the 

 cotyledons, or seed-leaves ; that the agents in tMs 

 inoculation are the zoospores produced either from 

 the conidia or the oospores ; that they do not enter 

 the stomata or pores themselves, but thrust out a 

 germinating tube, into the extremity of which the 

 contents of the zoospores pass; that when these 

 tubes have entered the stomata of the cotyledons 

 they branch and ramify, becoming a true mycelium, 

 from which fruitful parasites are developed; that 

 if a plant so infested hves through the winter, the 

 parasite lives with it, to vegetate again in the 

 spring. 



The immense number of zoospores capable of 

 being produced from a single infested plant is 

 almost beyond calculation. It is easy for a million 

 of conidia to be developed from such a plant, each 

 producing from five to eight zoospores, besides a 



