Eyysiphe Polygoni. G. 0. Searle. 285 



The above results show that the "biologic form" of Erysiphe 

 Polygoni on cultivated Brassicae is able to live and produce 

 conidia when sown on the internal tissue of its host instead of 

 the epidermis. Further that when the form on varieties of 

 Brassica campestris was sown on varieties of B. olcracea, which 

 had been injured by cutting, full infections resulted instead of 

 the usual " subinfections." It is also of interest to note that in 

 some cases (e.g. A 7 and A 15) the cells of the host underwent the 

 typical discolouration even though a full infection finally 

 resulted; this discolouration was more notable however when 

 the mycelium spread to the uninjured epidermal cells. 



In view of the difficulty of keeping cultures of species of 

 Erysiphe for any length of time owing to its obligate parasitism, 

 it is worthy of note how useful the cut stem of Marrow-stemmed 

 Kale was found to be. This material kept remarkably fresh 

 in a large Petri dish on wet filter paper and, on the whole, 

 remarkably free from saprophytic fungi. As an instance it 

 may be noted that a piece of cut Marrow-stemmed Kale stem 

 after fifty-nine days in a Petri dish showed a perfectly healthy 

 patch of new mycelium with numerous chains of ripe conidia. 



By carrying out the inoculations in December, taking pieces 

 of Marrow-stemmed Kale from plants distant from those 

 carrying subinfections, and by sterilising Petri dishes, it was 

 possible to reduce the chances of natural infection to a negligible 

 quantity, especially as the inoculations were carried out on 

 freshly cut surfaces. 



The second series (B) was carried out in extension of the first 

 and also to test the viability of the conidia produced in series A. 



This series shows the full viability of conidia produced by 

 mycelium on cut surfaces; also that the distinctive discoloura- 

 tion cannot be entirely correlated with the source of the conidia 

 in the first generation. 



As in Series A the inoculations on uninjured Marrow-stemmed 

 Kale seemed to fail under cultural conditions and Brussels 



