72 Stevens — Science of Plant Pathology. \_June 



weeds and crop plants. The life histories of all disease pro- 

 ducing fungi must be closely studied, particularly to deter- 

 mine their hibernating condition. As yet the merest begin- 

 ning has been made. The interrelation of host and parasite 

 must be studied, the periods, points and modes of infection 

 made known. The biology of the fungi, their life habits, 

 conditions of spore formation, characters of growth, relation 

 to light, heat, moisture, nutriment, etc.; their resistance to 

 adverse conditions, their longevity under various conditions 

 of environment are all problems of ultimate practicality. 

 The question of species is unsettled and the recent demon- 

 stration of biologic varieties among the rusts, mildews and 

 fusariums opens a large and important field of research. The 

 agencies operating as disease distributors, the wind, insects, 

 soil, man, water or what not must be known that such distri- 

 bution be more readily controlled. The causes of resistance 

 and susceptibility to certain diseases rest in obscurity, except 

 in a few cases where the responsibility has been fixed upon 

 some particular structure or chemical. The breeding of 

 plants resistant to specific diseases not readily amenable to 

 other means of control must proceed. Such work is now in 

 progress with cotton, melons, tomatoes, tobacco, grains, flax 

 and other plants. The relation existing between many root 

 fungi and bacteria and the roots they inhabit remains to be 

 studied. Aside from parasitism there is also mutualism, a 

 kind of beneficial disease falling to the province of plant 

 pathology. It needs much further study. 



Specific problems also abound, the peach yellows and ros- 

 ette, the mycoplasm theory of rusts, the grape Brunnisure. 

 Differences of opinion now exist or the technique or scientific 

 data are insufficient for an adequate solution of these ques- 

 tions and many other similar ones. Work on timber protec- 

 tion, while not strictly a question of disease, but rather a 

 post-mortem problem, falls to the lot of the pathologist for 

 the want of a more appropriate place. That intensive study 



