

i9i 73 STEVENS— PLANT PATHOLOGY 303 



room for a complete "epidemiological" study of any one of many 

 really serious diseases. 



A large field involving knowledge of extreme value and demand- 

 ing ingenuity of experiment is that of pathogen transference. We 

 know a little about transference by insects, but very little about 

 wind and other agents. 



Fungicides and their action are in need of more study. It 

 is remarkable if accident has really given us the best fungicides in 

 copper sulphate and lime sulphur. Our knowledge of their action 

 and of their composition can be increased; so, too, the time to 

 apply them and the strength to use. The exact time of application 

 is undoubtedly of much importance; in some diseases, notably 

 apple rust, the variable results are presumably linked with the 

 time relation. Exact knowledge of such relation is needed in 

 many cases. The subject of fungicide injury to fruits or foliage 

 also arises here. 



There are many diseases which have been described in a pre- 

 liminary way, the causes of which are not yet known. Some of 

 these are of great injury, notably the various so-called "mosaics," 

 peach yellows and rosette. Their list is essentially included in the 



com 



It is 



for 



not too much to hope that some of these will give up their se 

 under proper attack; some seem to have done so recently; 

 example, beet curly- top and the crown-gall. The status of others, 

 such as Jonathan spot, tomato blossom-end -rot, tobacco mosaic, 

 and numerous other mosaics, is not so clear. There is here opportu- 

 nity for good descriptive work that we may know definitely with 

 what conditions we have to deal. When the anatomical, histo- 

 logical relations are definitely recorded, we shall at least be able to 

 classify these various types, and to know, for example, whether 



mosaic 



or different nature. Abnormal enzyme 



planation 



s 



lack conclusiveness, and certainly lack practical application. 



remark 



I have 



desired rather to indicate the need of intensive, thorough study 



ems 



