CHAPTER XVI. 



WHITE-RUST DISEASE OF CABBAGES, ETC. 



Cystopus candidus, Lev. 



THERE is no more familiar parasite of cruciferous plants 

 than the fungus of White Rust, Cystopus candidus, Lev. 

 The generic name is derived from Jcystis, a bladder, and 

 pous, a foot ; candidus, of course, refers to the white 

 colour of the fungus ; the name is intended to indicate the 

 white pustular appearance of the fungus on the attacked 

 plants. White rust is extremely common on cabbages, 

 excessively so on the common Shepherd's-purse, Capsella 

 Bursa-pastoris, D.C., and many other cruciferous weeds 

 and garden flowers. The appearance of the fungus is 

 known to every one who has walked in a kitchen garden. 

 Cabbages and cauliflowers are seen with their leaves and 

 stems swollen, distorted, and spotted with white streaks and 

 blotches, as if sprinkled over with whitewash. If typical 

 examples of the parasite are carefully examined on in- 

 vaded leaves, it will be noticed that the white splashes 

 are really somewhat elongated swollen pustules, often 

 arranged in a concentric or spiral manner, and measur- 

 ing half an inch or more across. On the leaf stalks and 

 flower stems the pustules are disposed in a more irregular 

 manner. The parasite invades every part of the host 

 plant above ground, sometimes sweeping off every seedling 

 in the earliest stages of growth, at other times attacking 

 the flowers, and so stopping the production of seeds. The 

 fungus, in whatever form it appears, reduces and damages 

 the produce of the plants attacked. Experienced observers 

 can detect the presence of white rust long before the 



