PLANT PHYSIOLOGY. 47 



This does not, however, complete the story. The fungus 

 may be successful in penetrating the skin of the plant, but its 

 difficulties have then only begun. It has to break down the 

 plant tissues, and secure a supply of food for its growth and 

 reproduction. To do this it must manufacture a chemical 

 solvent known as an enzyme. By means of this enzyme it can 

 break through the network of partitions underlying the skin 

 of the plant, which form, so to speak, the skeleton in which 

 the " flesh " of the plant — the protoplasm — is suspended. Thus 

 we have another reason why some plants are attacked and others 

 not. In the former case, the fungus is able to manufacture the 

 enzyme which breaks down the internal framework of the plant ; 

 in the latter case, it cannot, and so it makes no progress. 



Assuming, however, that the fungus spore has satisfactorily 

 :-germinated, has penetrated the skin, and by manufacturing an 

 appropriate enzyme has gained access to the plant juices, it 

 may still be unable to continue, for unless it can live on those 

 juices it must perish. This constitutes a third reason for 

 immunity; a plant is safe from serious infection if its juices are 

 unpalatable to the fungus. It is this part of the problem which 

 is under investigation at the moment. What is it that makes 

 certain plant juices so distasteful to a fungus that it will die 

 rather than partake of them ? Why, for example, does Botrytis 

 parasitica thrive on the onion and die on the apple; and why 

 does Monilia cinerea flourish on the apple and refuse to live 

 on the onion ? The examination of this and similar problems 

 is still only in an early stage, but it has been shown that, in 

 addition to cases where the fungus will not begin its growth 

 at all in a particular plant- juice, there are other cases where it 

 will begin to grow quite well, but sooner or later poisons itself 

 by its own waste-products. A good deal more remains to be 

 learnt, but when all the phenomena of this hfe and death struggle 

 — as vital for the farmer as for the fungus — have been investi- 

 gated and explained, we shall have a complete history of the 

 physiology of fungus attack, of an importance which can hardly 

 be over-rated. 



Electrical Treatment of Crops. 

 Some years ago a Swedish Professor who was on a visit to 

 the Arctic circle was struck by the rapid summer growth of 

 plants in those regions during the Arctic summer, and began 

 to wonder why. It could hardly be due to excess of sunlight, 

 because the sun is always low, and its rays strike the ground 

 at an oblique angle. He was led to the view that the electrical 

 conditions were abnormal near the poles, and that the plants 



