DISEASES «»!•' PLANTS. '259 



DISEASES OF PLANTS. 



Report of the botanist, <i. I'.. Stone and N. I'. Monah w | Massachusetts Sta. /.'/-/. 

 1904, /'/>■ 7-84, dgms. ?). A reporl is given of the investigations carried on by the 

 botanist and bis assistant, mosl of ili<' work being conducted in the greenhouses in 

 connection with the cultivation and diseases of roses, carnations, violets, tomatoes, 

 and melons. 



Brief reports are given on field investigations, and it is stated thai a&paragus rusl 

 was more prevalenl than during the previous year. < lonsiderable damage is reported 

 to cultivated dandelions by stem rot, and the cucumber and melon blight, which have 



been previously quite troubles \ during the season reported upon were hardly 



observed at all. The worst injuries reported were due to winterkilling and the 

 effect, as shown upon various Bhrubs and trees, is described. 



In continuation of previous work, the authors have carried on experiments in 

 soil sterilization, and in the present report a resume* is given of tin- results obtained 

 from this practice. Sterilization has proven a satisfactory means for lessening the 

 amount of infection in lettuce houses where the plants were affected with drop and 

 Bhizoctonia, and also as a m sans of ridding them of nematodes. It was found that 

 sterilization of the soil modifies the texture of lettuce, having a decidedly stimulat- 

 ing effect. 



In connection with tin- stimulated growth, plants are somewhat more subject to 

 disease and on this account greater attention must be given the ventilation and tem- 

 perature of the houses. It is believed by proper ventilation and watering that the 

 Botrytis rot of lettuce can he eliminated to a great degree. With cucumbers, sterili- 

 zation of the soil was found to force the plants to a considerable extent, especially 

 when under favorable conditions regarding light. 



Where the conditions of growth are abnormal the sterilization was without any 

 value in stimulating growth. A decidedly beneficial effect on the growing of carna- 

 tions was shown where sterilized soil was used, the amount of disease being greatly 

 reduced. No detrimental influence on the soil itself has been observed in the exten- 

 sive series of experiments which have been carried on at this station. 



In continuation of previous, investigations ( K. S. \l. Id, p. :;:;.*> i, a report is given 

 on the influence of electrical potential on the growth of plants. Comparisons were 

 made of the growth of roots and tops of radishes when electrified and when not sub- 

 jected to such treatment, which show that the leaves of the electrically treated plants 

 were quite different from those of the normal ones. The electrical stimulation 

 seems to give rise to conditions similar to those caused by lack of light which 

 results in a partial etiolation. 



Comparisons are reported of the atmospheric electrical potential in trees and in 

 the free air. which shorn that some trees have a greater tendency toward conducting 

 the electricity from the air to the earth and others have a tendency for conducting the 

 electricity from the earth t<> the air. In all probability the exchange of electricity 

 from the earth to the air or vice versa does not take place at the same time from the 

 same tree. It is probable that some trees always conduct electricity from the air to 

 the earth, while others conduct electricity from the earth to the air; and it is also 

 probable that in the vicinity of large trees there may he a detrimental influence to 

 crop- and vegetation in general which can not he accounted for by lack of sunshine 

 or soil moisture. 



References are given to the more important literature relating to diseases of crops 

 which are believed not to he caused by fungi or insects. This is supplemental to the 

 previous publications of the Connecticut state station | E. 8. R., 5, p. 1078; L3, p. r>4 . 

 The lUt i> intended to supplement those previously mentioned and to give the more 

 important publications of the experiment stations and the United states Department 



