244 EXPEElMENff STATION EECOED. 



Since air-dried western yellow pine lumber checks so badly, it pays to kiln 

 dry all of the upper grades. Approximately 80 per cent of western yellow pine 

 tallied in this study retained the original grade as made at tbe mill after tbe 

 lumber had been kiln dried and surfaced. The average loss through deteriora- 

 tion during kiln drying of the upper grades was approximately $1.55 per thou- 

 sand board feet. With lumber surfaced on two sides there was a further loss 

 ranging from 51 cts. per thousand board feet in lumber taken directly from 

 the kiln to $2.27 per thousand board feet in that stored in the sheds. 



Experience has shown that kiln drying is the only practical method of keeping 

 up the grades of Douglas fir. Approximately 91 per cent of the upper grades of 

 Douglas fir 1 in. in thickness retained, the original grade when shipi>ed after 

 being kiln dried. The average loss through detei'ioration due to kiln drying 

 was 53 cts. per thousand board feet for 1 in. lumber and $2.90 per thousand 

 board feet for 2 in. lumber, which checks very badly. 



DISEASES OF PLANTS. 



Physiolog'ical relations of powdery mildews to their hosts, G. M. Reed 

 (Missouri Sta. Bui. 131 {1015), pp. JfGfl, 1,70).— It is stated that absence of light 

 during the growth of barley and wheat results in a marked decrease of infection 

 by powdery mildew ; also a retardation in the development and a lengthening 

 of the incubation period of the fungus. A marked correlation is noted between 

 the violence of infection and the development of chlorophyll in etiolated plants. 



A connection between mildew attack and photosynthesis is indicated by the 

 fact that wheat and barley grown in the presence of light, but in* the absence 

 of carbon dioxid, remain free from mildew. Minei'al starvation of the plant 

 confers upon it partial immunity as regards the fungus, but it does so indirectly 

 by lessening the vigor of the host and so depriving the parasite of its proper 

 nutriment. Such substances as manganese sulphate, potassium sulphate, and 

 lithium bromid added to the soil may slightly decrease susceptibility in the 

 host. Dwarfing host plants by a high content of mineral in the soil water 

 has no effect as regards susceptibility to mildew. There seems to be a positive 

 correlation between normal development on the part of the host and successful 

 attack on the part of the fungus. 



Studies in the genus Phytophthora, J. Rosenbaum (Ahs. in Phytopathology, 

 4 (1914), No. 6, pp. 394, 895). — A study is reported of a number of species of 

 Phytophthora, 10 of which have been collected and grown in cultures. 



The results indicate that the kind of spores produced and the time of their 

 appearance on a given medium is in some cases characteristic of the different 

 species. Morphological studies also reveal characters of taxonomic importance. 

 A great variation was found to exist in spoi-e forms. From inoculation experi- 

 ments the author concludes that the parasitism of species of Phytophthora is of 

 a rather low order. 



The Verticillium wilt problem, C. W. Caepenter (Abs. in Phytopathology, 4 

 (1914), No. 6, p. 393). — Verticillium wilts are said to have been reported on 

 potato, okra, eggplant, snapdragon, and dahlia. 



Of the first three plants the parasite is said to be V. albo-atrum, while for 

 dahlia wilt the cause is given as V. dahliw. In addition to attacking the hosts 

 mentioned above, V. albo-atrum is believed to be the cause of a spontaneous wilt- 

 ing of two cotton plants at Arlington, Va. It likewise occurs in the vascular 

 system of the weeds Abutilon and Xanthium, and is also the cause of the wilt 

 of snapdragon. Attention is called to some views regarding the classification 

 of the genus and its species, and the desirability of a monographic study is 

 pointed out. 



