Page:Proceedings of the Royal Society of London Vol 69.djvu/481

Rh 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 experiments on seedlings started in pots of coir-fibre, under conditions more