W. F. Bewley 125 



dissolved in water, it retains its power of producing wilt. Heating for 

 5 minutes at 100° C. greatly reduces its activity, but does not entirely 

 de-activate it. 



Enzyme jyrodnction. 



The wide range of artificial media, upon which the several strains 

 of F. albo-atrum will grow indicates the probable secretion of a large 

 number of enzymes. Modifying the methods elaborated by Crabill and 

 Eeed (6) the following specific enzymes were determined : amylase, inulase, 

 emulsin, hpase, protease, erepsin and amidase. There was no good 

 evidence of cytase production under the conditions tested. 



4. Strains of Verticillium. 



From April 27th to May 25th, 1920, over 50 single-spore isolations of 

 F. albo-atrum were made. Small pieces of diseased wood were incubated 

 in a moist chamber and spores transferred from the fungus growth which 

 appeared to a drop of sterile water on a coverslip. Spore dilutions were 

 made into other drops until each drop contained one or two spores. 

 These drops were transferred to thin layers of potato agar in a petri- 

 dish and the position of each spore marked after examination under the 

 microscope. As soon as germination began the spores and young hyphae 

 were transferred to sterile tubes of prune agar. The resulting isolations 

 were classified into six groups varying in the rate, amount and kind of 

 growth, and in the production of colour, carbonised hyphae and micro- 

 sclerotia, when grown in Dox's solution with 1 per cent, saccharose. All 

 the groups have been tested for pathogenicity and there is some indica- 

 tion that the virulence of the strains is related to the ability to produce 

 carbonised hyphae and microsclerotia. Group I was uniformly slow in 

 producing the characteristic wilt, while group VI was most rapid in its 

 effect, as is shown in Table III. 



5. Range of Hosts. 



The host plants used were as follows: potato {Solanum tuberosum), 

 egg plant {Solanum melongena), snapdragon {Antirrhinum sp.), cucumber 

 {Cucumis sativus), sycamore {Acer sp.), cotton {Gossyjyium herhaceum), 

 pepper plant {Capsicum sp.) and elm {Ulmus sp.). In the first four a 

 definite Wilt Disease and subsequent desiccation was produced. In the 

 sycamore and cotton the plants were much stunted and the leaves withered 

 without wilting, but in the pepper the leaves wilted and remained green. 

 The plants were stunted in the latter case, but only a few leaves were 

 affected. 



Ann. Biol, ix 9 



