60 



SCIENCE 



[N. S. Vol. XXVIII. No. 706 



has an influence on fertility, the -whole ques- 

 tion may be greatly complicated. But such 

 complications seem to be irrelevant to the 

 simple issue raised by Mr. Yule's remarks. 

 G. H. Hardy 

 Tbinitt College, Cambeidge, 

 April 5, 1908 



P. S. I understand from Mr. Punnett that 

 he has submitted the substance of what I have 

 said above to Mr. Tule, and that the latter 

 would accept it as a satisfactory answer to the 

 difficulty that he raised. The "stability" of 

 the particular ratio 1:2:1 is recognized by 

 Professor Karl Pearson (Phil. Trans. Boy. 

 8oc. (A), vol. 203, p. 60). 



PURE CULTURES FOR LEGUME INOCULATION 



In the 1907 Eeport of the Biologist of the 

 North Carolina Agricultural Experiment Sta- 

 tion, Dr. P. L. Stevens and Mr. J. C. Temple 

 report some work upon cultures of the nodule- 

 forming organisms of legumes. The cultures 

 used were obtained from the United States 

 Department of Agriculture. The investiga- 

 tors have presented their data in such a man- 

 ner that the value of pure cultures for in- 

 oculating legumes appears questionable and 

 their conclusions emphasize their attitude of 

 disapproval. In carefully reviewing their re- 

 port, a very brief outline of which appeared 

 in Science, Vol. 26, 1907, p. 311, I have been 

 impressed with the fact that the inferences 

 drawn by the casual reader would almost cer- 

 tainly be unwarrantably antagonistic to the 

 use of pure cultures for inoculating legumes. 

 The investigators' objections to the actions 

 of cultures supplied by this department are 

 briefly as follows: 



A considerable number of the cultures 

 hermetically sealed in glass were sterile at the 

 time they were examined by Dr. Stevens and 

 Mr. Temple. The misconception in regard 

 to the viability of cultures distributed by the 

 department at the present time could have 

 been prevented by the insertion of a foot- 

 note explaining that since July, 1906, small 

 bottles with wax seals have been substituted 

 for small tubes hermetically sealed in the 

 flame of a blast lamp. It is surprising to 



me that four out of seven of the old-style 

 cultures examined by Dr. Stevens should have 

 been sterile, as my own investigations pre- 

 vious to adopting this method for distribu- 

 tion indicated that about one half of one per 

 cent, of the cultures sealed in this way in 

 routine work would be injured or sterilized 

 by the heat of sealing. The law of chance 

 must perhaps be invoked to explain the dis- 

 crepancy in our figures. It must be remem- 

 bered, however, that the cultures spoken of at 

 this time are the old-style liquid cultures, and 

 that the cultures distributed since July, 1906, 

 are not open to criticism of this sort. 



It is surprising to me also to learn that 

 during the multiplication period conducted in 

 the practical manner outlined for use on the 

 farm such great contamination should have 

 become manifest. Two years ago I had small 

 samples of these gross cultures prepared on 

 the farm returned to me by farmers in vari- 

 ous parts of the country for examination, the 

 sample being taken and mailed to me at the 

 time the culture was applied to the seed. 

 This, of course, allowed for greater develop- 

 ment of contaminations than would have 

 taken place at the time the culture was ap- 

 plied to the seed. Even with this handicap 

 about two per cent, of the cultures received 

 from the farmers were apparently pure, and 

 if contaminated the contamination was evi- 

 dently very slight indeed. About sixty per 

 cent, were contaminated, but not excessively 

 so, it being easy in all of these cases to iso- 

 late large numbers of Pseudomonas radici- 

 cola. The remainder were in rather bad con- 

 dition, although I doubt if ten per cent, of 

 the entire number received were so seriously 

 contaminated as to be worthless. 



The description of the pot experiments con- 

 ducted by Dr. Stevens and Mr. Temple is 

 confusing. In the first place, the sterilizing 

 of soil by heating is well known to injure the 

 soil seriously, and, regardless of the condition 

 of the nodule-forming bacteria introduced, it 

 is an open question whether soil sterilized by 

 heating would allow nodule formation until 

 a normal bacteriologic flora and normal soil 

 conditions generally had been reestablished. 

 It is impossible to determine whether any 



