11)11.] PUBLIC DOCUMENT — No. 31. 157 



wcakeiiiug; lliu.s the second year, and so on from year to year, 

 we have a general attempt to balance np the root system and the 

 leaf system. It is believed that this view is in accordance with 

 the trnth, although no specific Avork has been done here to prove 

 it other than general observations. 



Chemical Tests of Abnormal Leaves. 



In view of the fact that physiological diseases in general are 

 principally caused by derangement of the function of some 

 organ of a plant, as a result of poor nutrition (lack or excess of 

 some necessary plant food), it was thought that it would be well 

 to obtain, in a general w^ay. an idea as to the presence and ab- 

 sence of certain substances in the leaves of diseased plants. 

 Owing to pressure of other work it was necessary to use dried 

 specimens for examination. The specimens, however, were not 

 over one or two months old when the examinations were made, 

 therefore no great change of constituents could have taken 

 place, with the exception of loss of water, and this was not of 

 any importance. A complete analysis was not made of the 

 leaves, but comparative tests were made, comparing the sub- 

 stance in healthy leaves A\ith the same amount of diseased 

 leaves. The substances tested for were principally nitrates, 

 enzymes and starch. 



As Woods ^ in his bulletin on mosaic disease advances the 

 theory that it is caused by an excessive amount and increased 

 activity of oxidizing enzymes, such as oxidase and peroxidase, 

 equal amounts of leaves from healthy and diseased leaves were 

 tested to see if there w^as any increase or decrease in the relative 

 amounts i)resent. It was found that in general there was 

 usually present in diseased leaves a slightly larger amount than 

 in the healthy leaves, but it was not necessarily so, as in five 

 cases out of eighteen there was less present ; but this may pos- 

 sibly have been due to individual variation in the leaf itself, as 

 the method of taking equal weights of leaves for examination 

 has some drawbacks, but no better method has as yet suggested 

 itself. 



It was found that catalase, another ertzyme which was discov- 



' Loc. cit. 



