136 The Ottawa Naturalist [Dec. 



is exactly the same in plants. Plants are living beings subject 

 to all kinds of ills without being actually diseased, i.e.. being 

 attacked by a specific organism bringing about a pathological 

 condition. Prof. Marshall Ward of Cambridge, England, has 

 expressed himself very instructively on the subject of predis- 

 position to disease in plants. He refers to two plants of the same 

 kind as much alike as possible in every respect, size, condition, 

 development, etc., and goes on to say, "Picture to yourself one 

 of these plants growing under the most perfect conditions, 

 supplied with the proper amount of food, its roots expanding 

 into a well-ventilated soil, rich in humus and plant food, etc.. 

 and the other growing under absolutely reverse conditions." 

 The result will be in one case a strong healthy plant and in the 

 other, a poor weakened plant just strong enough to keep alive. 

 Now the conditions, not to say constitutions of these two plants 

 must be very different. Different modes of nutrition we know 

 produce different chemical changes within a living plant. And, 

 no doubt, this difference in the condition of the host plant is 

 accountable for its power of resistance or state of susceptibilitv. 

 There may be a number of other factors producing similar 

 differences in constitution or in composition, if this is more cor- 

 rect. A potato tuber sound and fresh, will remain free from 

 fungi if kept in an ordinary room, while one that has been 

 exposed to frost or steam heat for a moment will soon be covered 

 with mould fungi of various kinds. We know of course that we 

 have changed the chemical composition of the potato exposed 

 to frost or heat, but we have also partly destroyed its life. 

 The same may be said of Prof. Ward's "ill-treated" plants. 

 Together with the changes of the chemical composition, we have 

 reduced its vital power; hence, would it not be reasonable to 

 expect an increased resistance to disease if the vital power of 

 any living organism is kept up to the highest mark? That this 

 contention is fundamentally correct is amply proven by the 

 'fact that cultivated plants which we grow under conditions to 

 which they are not fully accustomed are, generally speaking, 

 more subject to disease, likewise as Europeans are much more 

 liable to disease in tropical climates and vice versa. Sudden 

 or even gradual changes frequently result in lowering the vital- 

 ity of a living organism. Cultivated trees are constantly subject 

 to such unnatural changes. 



I have endeavoured to explain briefly, in the foregoing 

 remarks, the life and nature of parasitic fungi. We have con- 

 sidered how fungous diseases are spread by means of the spores 

 produced by the causal organism, we know how different may 

 be their modes of fructification and that winter and summer 

 spores must be looked for in many kinds, and we have further 



