OCTOBEE 25, 1907] 



SCIENCE 



541 



tion may prove it to be untenable; but it 

 is to its credit that, besides tracing to 

 dynamical causes the existing distribution 

 of continent and ocean, it offers an ex- 

 planation of the difference between the At- 

 lantic and Pacific types of coast, it gives 

 indications of a possible account of those 

 alternations of sea and land which first led 

 to the study of geology, and it suggests an 

 origin for Charles Darwin's unknown 

 force, the operation of which is slow and 

 intermittent, but irresistible. 



A. E. H. Love 



PLANT PATHOLOGY '^ 



TouE secretary has asked me to review 

 as far as possible in ten or fifteen minutes 

 our actual knowledge of plant diseases, 

 the best methods of combating them, the 

 progress that has been made, together with 

 a suggestion or two as to some improve- 

 ments that may be expected in the future. 

 I have accepted the invitation, knowing 

 fully that I could not in so short a time 

 begin to cover so much ground with a 

 sufficient degree of thoroughness to give an 

 adequate idea even of the most important 

 bearings of pathology on horticulture, but 

 I concluded that the committee must have 

 had in mind that I would use their request 

 as an illustration of the greatest failing, 

 not only in pathological investigation, but 

 in the application of methods recommended 

 for the control of diseases, namely, too 

 much haste and lack of thoroughness. 

 These are failings incident to work in a 

 new country under great pressure, where 

 the field is large and the workers few. 

 There has been a good measure of economic 

 justification for the mistakes of the past, 

 and they are teaching us valuable lessons 

 for our guidance in the future. What we 

 need now is to study carefully these suc- 



" Paper read at the meeting of the National 

 Council of Horticulture, Jamestown, Va., Septem- 

 ber 23, 1907. 



cesses and failures and determine as ac- 

 curately as may be possible their causes as a 

 basis for improved practise. 



The old conditions are rapidly changing. 

 The new times require more careful and 

 intensive methods. 



One-crop farming, too short and un- 

 wise crop rotations, improper methods of 

 fertilizing and culture, with destruction of 

 humus and the life and fertility of the soil, 

 careless methods of propagation and seed 

 selection, the use of varieties not adapted 

 to soil and climate, and other limiting con- 

 ditions are responsible for loss from 

 diseases in a larger degree than is realized. 

 An orange, or plum, or peach, or apple, or 

 any other tree or shrub, whose cambium 

 responds to a few warm daj^s in winter or 

 early spring, is not a safe variety to plant 

 in localities where such warm periods 

 occur. Plants of northern range, accus- 

 tomed to respond to lower initial heat stim- 

 ulus, are thus subject to winter injury in 

 more southern latitudes. On the other 

 hand, plants of southern range planted 

 north start later, are less subject to late 

 frosts, but may be injured by early frosts. 

 These cold injuries are often hardly notice- 

 able, but they are sufficient to weaken the 

 plant and open the Avay for trunk cankers 

 and numerous other parasitic diseases 

 which the trees could otherwise resist. 



A soil slightly too acid or alkaline for a 

 particular variety, though not enough to 

 prevent growth, may nevertheless weaken 

 the root system, or, in fact, the whole 

 plant, making it subject to serious disease. 

 So also the moisture or temperature fluc- 

 tuations of the soil and its aeration may 

 be unfavorable to a particular variety, 

 making it less resistant to disease, if not 

 actually causing a pathological condition in 

 itself. Too little attention has been given 

 to these factors by the farmei-s and horti- 

 culturists as well as by the pathologists. 



