Eyysiphe Polygoni. G. 0. Searle. 



283 



liminary stages of the spread of the fungus on to a new host, 

 especially since, as it is shown later, the conidia formed on the 

 " subinfection " are fully viable. 



The first series undertaken in the laboratory was one using 

 conidia from the Swede and Rape. Inoculations were ])erformed 

 on leaves in water under a bell- jar. 



Table V. 

 Conidia from Swede. 



Date 

 Nov. 21 



Nov. 29 



Nov. 21 



Host used 

 Swede . . . 

 Turnip ... 

 Rape 

 Kohl-rabi 

 Swede . . . 

 Kohl-rabi 



Rape 

 Kohl-rabi 



No. of 

 inoculations 



4 



2 

 2 



No. of 

 infections 



+ 4 

 + 2 

 + 2 



+ 4 



Remarks 



Leaf died 



With discolouration 



Conidia from Rape. 



+ 2 

 ? 2 



This table shows the typical results already noted in Table I. 



Two experiments with conidia from "subinfections" on 

 Marrow-stemmed Kale were then tried; four inoculations on to 

 Kohl-rabi leaves gave four "subinfections" but with no visible 

 discolouration of the epidermis; four inoculations on to Swede 

 leaves gave four full infections. These two experiments prove 

 the viability of conidia formed on "subinfections." 



It was now decided to carry out several series to test how far the 

 fungus could adapt itself to continued life on the internal tissues 

 of various hosts and to observe if any differences in infective 

 power took place under such conditions. These series were 

 carried out in large Petri dishes lined with moist filter paper, 

 and kept at a temperature varying between 50-60° F. 



The following abbreviations are used: 

 "Cut M.S.K." = A piece of stem of Marrow-stemmed Kale 

 approx. 3 inches long and li inches diam. cut in half 

 lengthwise, so that it is about f inch thick and then a sloping 

 cut made in the upper uninjured surface to remove a wedge- 

 shaped piece of tissue, leaving the internal tissue exposed 

 to about I inch deep. Conidia were then sown on the internal 

 surface thus exposed. This was found to be a convenient 

 size to use in large Petri dishes and kept fresh a long time. 

 "Cut ... petiole "= A piece of petiole, of host used, about 

 2 1 inches long with a wedge-shaped piece cut out leaving 

 internal tissue exposed to ^ inch deep. 



