Plant Sanitation. 



554 



[December, 1908. 



this loss, and much more will be done 

 when more scientific and detailed study- 

 is carried on by a larger number of in- 

 vestigators scattered widely over the 

 country. A conservative estimate of the 

 loss caused by the bitter rot of apples 

 throughout the country each year, is ten 

 millions of dollars. In the State of 

 Illinois, the loss, due to corn rot, for the 



East year, is estimated at perhaps two 

 undred and eighty thousand dollars. 

 But we want to know what may be done 

 to reduce such losses- It is a part of the 

 work of the plant pathologist to discover 

 how this may be done, and for many 

 diseases a remedy has been found. 



By proper spraying methods, on a 

 commercial scale, ninety per cent, of the 

 loss from peach yellows has been saved. 

 Oat smut has nearly lost its terrors for 

 the scientific farmer, because of the 

 method of " seed " treatment which kills 

 the smut spores. In New York a pro- 

 perly sprayed vineyard gave a net profit 

 of over fifteen hundred dollars more 

 than the same vineyard, unsprayed, 

 yielded the previous year. Diseases of 

 various origins have been treated, and 

 the loss caused by them has been 

 materially reduced. Moreover, the im- 

 portance of this work is increasing with 

 the growing population, for crops are 

 becoming more extensive and crowded, 

 a condition which gives two of the im- 

 portant factors that tend to produce 

 great epidemics of diseases. 



The science of plant pathology, like 

 bacteriology, is very closely related to 

 botany, and in a broad classification of 

 the sciences would be considered a part 

 of that great subject. Yet, with equal 

 justice, it may be considered as a separate 

 science, closely related, first to botany, 

 then to zoology, chemistry and physics. 



The affiliations with botany are varied 

 and strong. If we consider those diseases 

 which are caused by parasitic fungi, as 

 rusts, mildews and so forth, or by 

 bacteria, as many "wilts" of garden 

 plants, or even by the parasitic flowering 

 plants, such as the dodder and the 

 mistletoe, we must first know the names 

 and the systematic relations of these in- 

 vading organisms. Here at the outset 

 we come in touch with that great depart- 

 ment of the science, systematic botany, 

 which for very many years engaged the 

 entire attention of botanists. 



Hand in hand with this first part of 

 the investigation goes the study of the 

 morphology of the parasite, for to 

 determine the name we must know the 

 peculiarities of form and of structure 

 which distinguished it from all of its 

 relatives. Moreover, the parasite, if it 



grows on two or more different plants, 

 may show various modifications of its 

 own form, according to the plant on 

 which it happens to develop. Thus, the 

 common grain rust, Puccinia graminis, 

 when growing on its alternate host- 

 plant, the barberry, produces entirely 

 different kinds of spores from those on 

 the grains. Pathology and morphology 

 cross paths also at another point. A 

 large and important field of study now 

 being developed is that of the correla- 

 tion of the natural structure of the 

 plant attacked, with the modifications 

 due to the disease. This work is essen- 

 tial for two reasons. We may thus 

 learn, in regard to diseases caused by 

 organic beings, in what manner the 

 parasite attacks and destroys the host- 

 plant. A disease, however, may not be 

 caused by an organism, but may result 

 from certain known or unknown im- 

 proper physical conditions of the plant's 

 environment, Hence this study may 

 result in a better differentiation between 

 these so- called " physiological diseases," 

 and the derangements caused by 

 parasites. 



Plant physiology is no less important 

 in the study of plant diseases than 

 morphology. We must know the normal 

 functions of the plant attacked, and be 

 ableto reallzein what way they have been 

 deranged. 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 

 Sclerotinia 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 leaf- 

 spots, which remain localized in some 

 organ. When an organism has the 

 oower of injuring more than one kind of 

 plant, its own functions may bo modified 

 according to varying conditions. This 

 is important in seeking means of curing 

 or of preventing the disease. A good 

 example is the common grain rust 

 mentioned previously, which, though 

 identical in form and appearance, on 

 wheat, oats, and rye, cannot be taken 

 from any one of the three hosts and 

 grown on either of the others. 



Plant pahology not only owes much 

 to these departments of botany, but also 

 to bacteriology. Laboratory methods 

 which have been found useful in the 



