PESTS OF GARDEN VEGETABLES. 



803 



Cabbage White Rust. 

 Cystopits Candidas (Pers.), PI. VII. fig. 98 a, b. 



This is a very old and very common offender, and is not confined to 

 Cabbages, but extends its ravages to almost any Cruciferous plant. It 

 was described by Berkeley in 1848 as White Rust, and was then believed, 

 and long afterwards, to be related to the ordinary rusts, but recently, 

 when better known, it has found a place near the Rot Moulds. 



The external appearance consists of swollen, convex, white pustules, 

 sometimes in rings and patches, and sometimes scattered over all the 

 green parts. At first the cuticle is shining and unbroken, but at length 

 it is irregularly ruptured, to permit the spores to escape. The base of 

 these pustules consists of a mass of irregular, thick, knotted, mycelium, 

 from which arise club-shaped cells, bearing a chain of globose spores, 

 slightly attached to each other, and forming a kind of necklace, the upper 

 one falling away, and then the next, and so on in succession, as they 

 become matured (12-18 n diam.). 



Each spore or conidium when placed in water or a damp situation 

 undergoes just such a change as we have already described for the conidia 

 of the Rot Moulds (see Introduction, p. 2). From five to eight zoospores 

 are formed in the interior, and escape by rupture of the wall of the 

 conidium. Thus each conidium produces from five to eight active 

 zoospores, which finally serve to disseminate the parasite by infection. 



In the same manner also as in the rot mould does the internal 

 mycelium produce resting spores, which, after a period of rest, probably 

 through the winter, develop numerous active zoospores in the spring. 



In the present species the resting spores are globose (30-50 p diam.), 

 externally warted with large obtuse warts, and of a brown colour. 



This pest is distributed throughout Europe, and many parts of Asia, 

 Africa, and America. It may truly be said to be cosmopolitan. 



Sacc. Syll. vii. 792 ; Mass. PI. Dis. 59 ; Smith, Field Crops, 86 ; 

 Cooke, M. F. figs. 198-200 ; Cooke, Hdbk. No. 1564 ; " White Bust" 

 Journ. B.H.S. vol. hi. 1848, p. 265, with figs. ; Tubeuf, Dis. 123. 



Cabbage Black Mould. 

 Altemaria Brassicce (Berk.). 



This black mould was first described by Berkeley under the name of 

 Macrosporium Brassicce, and was found by him growing on cabbage leaves 

 in company with the common Cladosporium herbarum, of which he con- 

 sidered it to be probably a condition. The conidia are clavate, and 

 divided by from five to eleven septa, some of which have longitudinal 

 divisions, and are of an olive colour (60-80 x 15-16 /u). Subsequent 

 examination seems to have shown that the conidia are produced in short 

 chains, attached end to end, as is the case m Altemaria, and hence the 

 change of name. 



It is evidently very rare as a garden pest, although it has also been 

 found in France and Italy. The mould is developed on dry spots of dead 

 tissue, on cabbage leaves, and may probably be only a saprophyte, which 



B 2 



