642 EXPERIMENT STATION RECORD. [Vol 40 



was 48 hours. Biologic forms were found to be constant not only parasitically 

 but also morphologically, the morphologic stability being exhibited in the con- 

 stancy of size, shape, and color in the urediniospores of the particular form. 

 An exception is noted in the case of stem rust of oats, the shape and size of 

 urediniospores of which are very plastic. 



Common hosts which were found congenial to different biologic forms lacked 

 ability to unify them, as they were unable to exert any influence on spore 

 morphology. Uncongenial hosts almost invariably tended to decrease the size 

 of the uredinia and spores. 



In computing data and comparing results, the authors claim that it is neces- 

 sary to take into consideration the ecological conditions under which the rust 

 had been cultured. Adverse environmental conditions unfavorable for the host 

 are also unfavorable for the parasite, affecting the virulence and spore size of 

 the latter. The optimum atmospheric temperature for the development of the 

 rusts studied appeared to range between 6G.5 and 70° F. Sufficiency of water 

 and plentiful light were found indispensable for the best growth of the rust. 



The age of the host seedlings, provided they were healthy at the time of 

 inoculation, had no effect on the size of the urediniospores or the virulence of 

 infection. The length of association of a rust with its host, after the first 

 uredinia have burst the epidermis until teliospores are formed, did not Impair 

 the viability of the urediniospores nor exhibit any marked and consistent effect 

 on their size. 



New biologic forms of Puccinia graminis, E. C. Stakman. M. N. Levine, 

 and J. G. Leach (Jour. .{or. Research [I . S.], Hi {1919), No. 3, pp. 103-105).— 

 In a preliminary report on a study of new biologic forms of ]'. graminis on 

 wheat, carried on cooperatively between the Minnesota Experiment station and 

 the U. S. Department of Agriculture, the authors state that while a considerable 

 range of parasitism bad been reported previously, no tonus had been found 

 able to infect White Spring emmer and the durum variety Mindum, as wed as 

 several other varieties, mostly dttrums. By testing many species and varieties 

 it was thought that probably forms of rust could be found that would be 

 capable of attacking varieties resistant to all the known forms of stem rust. 

 This supposition has been verified, and a form has been found which infects 

 White Spring emmer anil Mindum normally. This work has been continued, 

 and during the summer of 191 s biologic forms were found, some of which are 

 virulent on many varieties of wheal, while others are weak and can attack 

 only a few varieties successfully. 



The wind dissemination of the spores of bunt or stinking smut of wheat. 

 F. D. Hkaud and D. C. Geobge ( Washington 8ta. Bui. tSl {1918), pp. 3 85, figs. 

 2). — The authors present some of the data on which a previous popular bulletin 

 was based (E. S. R., 40. p. 49). 



Asa result of several years' study, it is concluded that in southeastern Wash- 

 ington and adjacent regions the principal infection of wheat by smut is through 

 Wind-borne spores liberated at thrashing time. Positive evidence of the abun- 

 dant and wide dissemination of smut spores has been obtained by microscopical 

 studies of washings from leaves and by the use of spore traps exposed at con- 

 siderable distances from wheat fields. It is stated that during the thrashing 

 season there Is a smut shower or spore fall in the vicinity of Pullman, Wash., 

 which begins in August, the exact time of the maximum depending in part on 

 the location, on the period at which the thrashing operations are most numerous, 

 and also upon climatic factors. The dry conditions which prevail during the 

 thrashing season, together with frequent winds of high velocity and with a 

 cropping system winch includes summer fallow and winter wheat, have com- 

 bined to make wheat smut especially severe in the Palouse country. A groat 



