June 19, 1908] 



SCIENCE 



939 



but may result from certain known or un- 

 known improper physical conditions of the 

 plant's environment. Hence this study 

 may result in a better differentiation be- 

 tween these so-called "physiological dis- 

 eases," and the derangements caused by 

 parasites. 



Plant physiology is no less important in 

 the study of plant diseases than morphol- 

 ogy. We must know the normal functions 

 of the plant attacked, and be able to 

 realize in what way they have been de- 

 ranged. Thus, if a parasite is the cause of 

 the disease, it may bring about the death 

 of the host-plant in one or more of the 

 following ways: It may strangle the plant 

 by clogging the water-conducting vessels, 

 as in the bacterial "wilt" of melons, 

 already referred to. Again, it may give 

 out a poison which kills the protoplasm of 

 the cells affected, as De Barry describes for 

 one of the Sclerotmia diseases. The third 

 method is by absorbing the food, water or 

 the protoplasm itself, from the cells of the 

 host. This seems, at the present time, to 

 be the most common mode of attack, 

 especially in those diseases, like leafspots, 

 which remain localized in some organ. 

 "When an organism has the power of injur- 

 ing more than one kind of plant, its own 

 functions may be modified according to 

 varying conditions. This is important in 

 seeking means of curing or of preventing 

 the disease. A good example is the com- 

 mon grain rust mentioned previously, 

 which, though identical in form and ap- 

 pearance, on wheat, oats and rye, can not 

 be taken from any one of the three hosts 

 and grown on either of the others. 



Plant pathology not only owes much to 

 these departments of botany, but also to 

 bacteriology. Laboratory methods which 

 have been found useful in the latter have 

 been adapted to the somewhat different 

 needs of the former. The use of culture 

 media, though not so absolutely necessary 



for elementary work in pathology as it is 

 in bacteriology, is, however, very common, 

 and, doubtless, special media for special 

 organisms are more numerous here than in 

 the allied science. Since Dr. Burrill, of 

 the University of Illinois, demonstrated in 

 1879 that in one instance, at least, the 

 pear blight, a plant disease might be 

 caused by bacteria, many diseases have 

 been shown to be of similar origin, and 

 here, naturally, the pathologist becomes 

 very closely allied with the bacteriologist. 



Of more and more importance to the 

 country is forestry, on which, eventually, 

 large portions of the land must depend for 

 rainfall and for timber. With this is 

 closely allied our science of plant pathol- 

 ogy. There are many diseases of trees, 

 which, unless curbed, threaten the grow- 

 ing of forests. One need but to refer to 

 the "punk" disease of the longleaf and of 

 the shortleaf pines and to similar decays of 

 other forest trees, to justify this claim. 

 Indeed, this is so important that a forest 

 pathologist has recently been appointed by 

 the government to study these diseases 

 more carefully. It is unnecessary to dwell 

 upon the increasing importance of the sci- 

 ence to agriculture, for we have already 

 noted their close relation. 



We have seen that botany in all its 

 phases is intimately associated with the 

 study of plant diseases, but now we will 

 consider what other sciences have an in- 

 terest in it. 



We turn naturally to zoology as the sci- 

 ence next to botany, and in many ways it 

 may well be so considered. To plant 

 pathology it is related chiefly through the 

 pathological conditions which arise as a 

 result of the attacks of various worms, 

 insects and even higher animals. In this 

 way, many galls, such as the - well-known 

 oak-galls and the nematode root-gall, which 

 inflicts so much damage, originate. The 

 stripping of the leaves from trees, and the 



