October 21, 1910] 



SCIENCE 



535 



parasites may not be obtained from the 

 seed. Our survey covers every county in 

 North Dakota and extends into Alberta 

 and the wheat fields of Manitoba, Minne- 

 sota, South Dakota, Washington and Cali- 

 fornia and the winter wheat regions of 

 Indiana, Kentucky, New York and the 

 wheat regions of Ontario. The parasites 

 have been found in seeds imported from 

 Russia, Italy, France and Algiers, and 

 have been taken from samples of straw and 

 roots from almost every important wheat 

 area of Minnesota or North Dakota. I am 

 thus confident that I am not announcing a 

 crop destruction feature of local nature. 

 It is beyond the possibilities of this 

 paper to detail the various lines of experi- 

 ments bj' which these conclusions have 

 been made necessary, but I may state that 

 the three most destructive parasites, taken 

 in their order, are one or more species of 

 Hebninthosporium, one or more species of 

 Fusarium, the type of fungus which pro- 

 duces wheat scab and flax-wilt, and one or 

 moj-e species of Colletotrichum. These are 

 universal and effective on roots and leaves, 

 stems and seed, and various species of 

 Macrosporium and Alternaria are great 

 blighters of seed and destructive both on 

 the straw and on the grain, especially at 

 germination time. Our experiments have 

 gone so far that I may say that I can take 

 any type of soil in North Dakota and 

 Minnesota which will grow the hard spring 

 wheats and from it raise either a typically 

 diseased crop or plants of normal growth. 

 The methods of doing this are too "expen- 

 sive for farm operations. They consist 

 essentially in soil and seed sterilization, 

 whether it is done by chemicals or by heat. 

 "We have conducted persistent cropping 

 experiments for many different pure pedi- 

 greed strains of wheat upon twenty-seven 

 separate fertilizer plots, the strains of seed 

 for all plots being the same at the begin- 



ning of the experiment, after which each 

 plot has raised its own seed. These fertil- 

 izer experiments demonstrate clearly that 

 in the absence of knowledge of the pres- 

 ence of the diseases no one could draw 

 any reliable conclusion as to what crop 

 they might cause to develop in any partic- 

 ular year. They do, however, demonstrate 

 that various types of fertilizers have more 

 or less effect upon the development of the 

 diseases and of the crop, and that the me- 

 chanical condition of the soil has much to 

 do with the development of both crop and 

 diseases, and that whenever there is a 

 tendency to check the development of the 

 disease in the straw there is a tendency to 

 produce plump seed. For example, the ad- 

 dition of phosphates does not seem to do 

 away with the actual presence of the para- 

 sites in the soil, but it does enable the straw 

 to ripen plump seed. The proper conclu- 

 sion is not that the soil is necessarily defi- 

 cient of phosphates, but that, the soil being 

 infested with parasitic fungi, the addition 

 of more phosphates tends to harden the 

 straw in the same sense that a harsh dry 

 atmosphere, such as some of you people are 

 interested in, and such as North Dakota 

 has suffered intensely from during the 

 past season, tends to harden the straw and 

 make plump wheat, though it does not of 

 necessity mean a large number of bushels. 

 I have this season seen fields that were so 

 diseased with these root parasites that, in 

 association with the drought, the wheat 

 did not grow high enough to reach the 

 sickle bar, and yet there was plump wheat 

 from such sick plants. Whenever such 

 sick areas received a reasonable shower or 

 the soil was so cultivated as to conserve the 

 moisture, there was an increase of bushels 

 and a decrease of quality, due to shrivel- 

 ling of the grains. The fungi are s» 

 constituted that they appreciate a highly 

 vegetative tv'pe of straw, and when there is 



