WHITE RUST. 



Cystopus candidus Lev. 



PRELIMINARY. 



THIS isavery common parasitic fungus, forming white 

 patches on the surface of the leaves, stems and flowers 

 of many cruciferous plants, such as various species of 

 Capsclla, Sisymbrium, Lcpidium, Nasturtium, Sinapis, 

 and Raphanus. It is especially abundant upon Cap- 

 sella or shepherd's purse, 1 from early spring till late 

 in the fall, whitening and distorting the stems, leaves 

 and flowers. Yet, notwithstanding such luxuriant 

 growth, the sexual condition with resting spores is not 

 abundantly found on this host, but is, however, 

 produced in great luxuriance inside the flowers and 

 flowering branches of radish (Raphanus), causing 

 them to become enormously enlarged, sometimes even 

 two to five centimeters (one or two inches) across (see 



fig- 3). 



It is possible, with patience and care, to make out 

 the parts without the use of chlor-iodide of zinc, but it 

 affords so much assistance that it ought to be used if 

 obtainable. 



The requisites for the following study are branches 



1 Fora description of shepherd's purse see p. 222. 



