938 



SCIENCE 



[N. S. Vol. XXVII. No. 703 



both of form and of function, whicli in 

 animals are, and in plants may be, called 

 diseases. There is one other phase also 

 which must always appear, that of the pre- 

 vention and the cure of the maladies. 



Few people who have not studied the 

 matter realize the very large loss of money 

 occasioned each year by these plant 

 diseases, and fewer yet know that much 

 has already been done to diminish 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 past year, 

 is estimated at perhaps two hundred 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 com- 

 mercial 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 properly sprayed 

 vineyard gave a net profit of over fifteen 

 hundred dollars more than the same vine- 

 yard, unsprayed, yielded the previous 

 year. Diseases of various origins have 

 been treated and the loss caused by them 

 has been materially reduced. Moreover, 

 the importance of this work is increasing 

 with the growing population, for crops are 

 becoming more extensive and crowded, a 

 condition which gives two of the important 

 factors that tend to produce great epi- 

 demics 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 rela- 

 tions of these invading organisms. Here 

 at the outset we come in touch with that 

 great department of the science, systematic 

 botany, which, for very many years, en- 

 gaged 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 deter- 

 mine the name we must know the pecul- 

 iarities 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 de- 

 velop. Thus, the common grain rust, 

 Puccinia graminis, when growing on its 

 alternate host-plant, the barberry, pro- 

 duces 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 

 correlation of the natural structure of the 

 plant attacked, with the modifications due 

 to the disease. This work is essential for 

 two reasons. "We may thus learn, in re- 

 gard to diseases caused by organic beings, 

 in what manner the parasite attacks and 

 destroys the host-plant. A disease, how- 

 ever, may not be caused by an organism^ 



