1911.] PUBLIC DOCUMENT — No. 31. 159 



attacks of leaf-sucking insects, such as aphis, etc., as in a few 

 instances specimens of diseased shoots were obtained which 

 showed the effects of these insects, and some aphides were found 

 also. Xo insects were observed, however, on healthy shoots, or 

 to so great an extent on shoots which had only a slight indica- 

 tion of the disease in question. It appears from our observa- 

 tions that the disease renders the shoot more liable to the 

 attacks of insects on account of its weakened condition, in some 

 respects it being far more normal ; also, the attacks of insects 

 intensify the disease by taking from the leaf a large amount 

 of proteids and sugars. The effects of insects have been noted 

 by various authorities, among which may be mentioned Woods ^ 

 and Suzuki.- More specific and interesting facts on this point 

 might be brought out by further observations and detailed study 

 in conjunction with entomologists, but this is without the sco])c 

 of the present paper. It is, however^ true that insects seem to 

 prefer a diseased leaf to a healthy one under these conditions. 



More purely chemical w'ork would undoubtedly be of great 

 interest in connection with this interesting disease, and no doubt 

 will find a place in a future report, but it is thought that 

 enough has been done wath the disease to bring out several new 

 points in regard to it. 



Conclusions. 



(1) The abnormal condition of leaves, showni by severe dis- 

 tortion and increase in number, and also sometimes in size, may 

 be classed under the malnutrition diseases, due to functional 

 derangement, as no fungi or bacteria have been found associated 

 with it. It must therefore be due to internal conditions, such 

 as an abnormal metabolism. 



(2) It is allied to those pathological conditions which may 

 be brought about by excessive use of nitrates or overfeeding. 



(?>) Tt is not allied to mosaic disease, which it somewhat re- 

 sembles, as this is capable of transmission from one plant to 

 another, and in no case have we been able to bring this result 

 about by inoculation with tissue of malformed leaves. 



(4) From our observations it is not of a permanent character, 



' U. S. Dept. Agr., Bur. Plant Ind., Bui. No. 18. 

 ! Gen. Bui. Col. Agr., Tokyo, Vol. IV., No. 4. 



