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FREDERICK H. BLODGETT 



associated with a difference in the natural defense by the host 

 against invasion. A common type of defensive structures is 

 either a thickening of the exposed walls of leaf cells, or of the 

 formation of a waxy substance upon the leaf surface. In either 

 case the susceptibility to leaf diseases is less than in unprotected 

 forms. 



Plant physiology gives the life processes of the healthy plant, as 

 a basis for the study of the deranged activity in the diseased speci- 

 mens. It, therefore, is an important element in the study of 

 diseased plants; since the behavior of the diseased specimens, the 

 changes produced in the tissues by the parasite, and the natural 

 means of protection are all better understood through the physio- 

 logical changes produced, than as separate facts. Treatments are 

 often determined by some physiological feature of the plants con- 

 cerned, and injury may be, traced to a physiological detail. 



Horticulture, in so far as it has to do with the general work of 

 plant propagation and fruit raising, is a closely related subject — 

 for one can best recognize diseased conditions after he knows well 

 the appearance in health, both of the growing plant and of develop- 

 ing fruits. A knowledge of the rules of plant breeding may ena- 

 ble one to add disease resistant qualities to some variety valued 

 for its fruit, and thereby gain an immense advantage in the fight 

 against loss by parasitic fungi. 



Chemistry is brought to the aid of the plant pathologist in find- 

 ing the exact composition of spraying solutions, and in the more 

 complex questions that have to do with the changes within the 

 plant cells under the influence of the invading organism. Recent 

 studies as to the changes which occur in spraying materials, 

 made up from identical stock solutions but differently handled, is 

 a case in point. Such fundamental factors as water requirement 

 vary greatly between healthy and infested plants, in a majority 

 of cases. 



IMPORTANCE OF THE COURSE 



Before discussing the make-up of a course for a particular in- 

 stitution, it may be helpful to review the work in the other land 

 grant colleges in the same subject. 



