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RETTF.WS. 
observation and exact experiment go a long way to discourage 
perfunctory explanations, which so often do duty for careful 
investigation, and lead to the employment of empirical remedies. 
Each page in many chapters touches on so many points on which 
our knowledge is yet insufficient that we might suggest that an 
interleaved copy, in which the observer either in the field or laboratory 
could note down pertinent facts, should in many cases lead to the 
record of many minor observations, which would otherwise be lost. 
Professor Ward objects to the division of plant diseases into 
“ physiological ” and “ parasitic,” since all disease is physiological in so 
far as it consists in disturbance of normal physiological functions. 
The separation into two groups, those induced primarily by physical 
causes and those due to the effects of a parasitic organism, is sound both 
systematically and for practical purposes, but “ environmental ” is 
perhaps a more accurate name than physiological. 
The whole question of grouping of diseases in plants is one of great 
difficulty, and even the sub-grouping of the diseases due to specific 
parasitic organisms is not easy. The method of arranging the diseases 
by the natural order of the organisms causing them is plain sailing in 
the case of diseases attributable to one chief and primary cause, 
but does not help where one or more factors are correlated. There is 
a chaos at present, and a system would be welcome, even if somewhat 
arbitrary, which would aid the collection of data and pave the way to 
a rational arrangement. In the book before us such grouping as 
“ artificial wounds,” “ natural wounds,” “ excrescences,” “ exudations,” 
“ monstrosities,” is open to various objections. 
In the chapter on the spreading of disease nearly all agencies which 
have been suspected or proved to directly distribute spores are 
mentioned, and here we have a field of investigation possessing 
attractive interest and of direct economic importance. If we take the 
question of wind agency alone, we have a number of phenomena, 
which, if properly understood, would lead us far on the road of 
preventive sanitation. 
Observation of meteorological conditions will bring much informa- 
tion of value in forming a clear conception as to the means of 
distribution of various parasitic fungi. The study of wind currents, 
succeeded by moist atmospheres, flights of insects, itineraries of 
animals with regard to their porterage of spores, will give results 
which enable us to determine the best way of dealing with protective 
wind belts of trees and selection of safe places for the cultivation of 
plants specially liable to attacks of parasitic organisms. 
It is not to be expected that in such a small book on so large a 
subject everything can be included ; some mention, however, of the 
factors in nature which make for the success of the host plant in its 
fight against the parasite would have added to the completeness and 
interest of the book. 
