Page:Proceedings of the Royal Society of London Vol 69.djvu/486

466 These results also accord with the appearance of the plants them- selves. The want of Po0 5 results in a long limp growth, and very pale colour, and the attacked spots show corrosion and collapse instead of normal flecks.

Similarly, in plants deprived of K we have pale collapsing patches in place of normal flecks, though the plant is not drawn and etiolated as in the previous case. Where Mg was wanting the drawing and paleness of the leaves were not so marked, and the fungus flecks in the positive case were more like the normal.

That a want of supplied Ca should have very little effect on either host or parasite, was no doubt due to there being small quantities available in the soil and pots. The flecks and pustules were apparently normal, though small.

It is not easy to see why the pots with water only yielded plants with flecks as good as, or even better than those with normal solution, unless the concentration of the salts affects the fungus. However it is probably not to be inferred that in any of these cultures the grass was totally deprived of the given salt it would get traces from the pots and coir in any case but the effects of deprivation of salts ought certainly to be felt, and I think were so to some extent in lengthening the incubation period.

So far as the results go they suggest that differences in the supply of minerals affects the development of mycelium and of spores owing to effect on the host in cultivating the host we also cultivate the parasite.

But I would insist that these trials with special mineral-supplies are merely preliminary. The task in hand was far too extensive for the problems to be solved in one season, and I contemplate carrying the whole matter or persuading some one to do so much farther in the future. Meanwhile, the results give suggestions for further work, and much remains to be done along the lines I have here laid down, as well as in directions yet to be opened out.

The results of an extended series of observations upon this phe- nomenon have led the author to conclusions which may be summarised as follows :