of a Urcdine, Puccinia diepersa (Eriks.). 



The following experiment (Table VI) 

 seems at first sight very suggestive in 

 its definite results, but much more 

 work will be needed before we can 

 generalise widely. Five tubes with 

 bulbs below were charged with a seed- 

 ling each of B. arvensis and five with 

 . velutinus, one of each five tubes 

 having normal Detmer's solution, one 

 the same minus K, Ca, &c., respectively. 

 The seedlings were 10 days old, grown 

 antiseptically on moist filter paper, 

 and therefore exhausting the reserves, 

 and would probably come at once 

 under the full influence of the mineral 

 solutions. 



Each seedling was infected forthwith 

 with spores from B. mollis, tested, and 

 found to be not very vigorous in 

 germination. Since all were infected 

 alike, however, on the first leaf and 

 from the same batch of spores, I think 

 we must regard the results as fairly 

 comparable. 



As the table shows, every plant of 

 B. velutinus had spore-bearing pustules 

 in 10 11 days, whereas the B. arvensis 

 gave no signs, if we except one doubt- 

 ful pustule on the llth day in the tube 

 devoid of potassium. 



It seems necessary to conclude from 

 this series that B. arvensis is far less 

 easily infected than B. velutinus under 

 any conditions of mineral supply 

 afforded. The experiment also shows 

 that. in the case of a susceptible plant 

 such as B. velutinus, no appreciable 

 effect is produced by the mineral 

 supply in the short time (10 11 days) 

 occupied in incubation. Something 

 may turn out to be due to the differ- 

 ences in size of the seeds, however. 



Meanwhile I had made some expe- 

 riments on seedlings started in pots 

 of coir-fibre, under conditions more 



461 



