Mat 19, 1911] 



SCIENCE 



781 



are unsatisfactory to use, because of the un- 

 certain factor of variable climatic conditions 

 from year to year; but some comparisons 

 might have been made between the yields ob- 

 tained during recent years from land that has 

 long grown wheat and the yields on virgin or 

 nearly new fields on similar soils. Or, lacking 

 such data, it would have been helpful to the 

 reader had there been given some statement as 

 to the present wheat yielding capacity of the 

 fields from which the samples were obtained. 



Unless it is shown definitely that the main- 

 tenance of the nitrogen and humus content of 

 these Cache Valley soils is correlated with the 

 maintenance of their wheat yielding capacity, 

 these investigations lose much of their pos- 

 sible value. 



As to the matter of the farming methods for 

 wheat production on this Cache Valley land, 

 it is the general practise to harvest the grain 

 with a header or with a combined harvester 

 and thresher, either of which implements 

 leaves on the land the major portion of the 

 grain straw, which is subsequently plowed 

 under.^ Mr. Stewart makes incidental refer- 

 ence to this feature of the agricultural prac- 

 tise in the Cache Valley, but he does not make 

 it clear that in this respect that practise is es- 

 sentially different from what it is in the dry- 

 land wheat regions of the Great Plains and 

 eastward, where it is the custom to harvest the 

 grain with a binder and remove the larger 

 part of the straw. This omission seems par- 

 ticularly unfortunate, in view of the general, 

 and possibly misleading, inferences that may 

 be drawn from Mr. Stewart's otherwise valu- 

 able contribution to knowledge. If, as it seems 

 reasonable to believe, the true explanation of 

 the observed humus maintenance lies in the 

 practise of plowing under each year the large 

 amount of wheat straw, it becomes apparent 

 that similar results are not to be expected 

 where a similar practise is not followed. 



C. S. SCOFIELD 



U. S. Depaetment or Agriculture, 

 January 14, 1911 



" See Bulletin No. 103, Bureau of Plant In- 

 dustry, U. S. Department of Agriculture, pp. 31- 

 35, issued May 31, 1907. 



SPECIAL AETICLES 



SOME EXPERIMENTS ON THE PRODUCTION OF 

 MUTANTS IN DROSOPHILA 



MacDougall has reported the successful 

 production of mutations by treating the 

 ovaries of certain plants chemically or os- 

 motically. As long as the full account of his 

 results is not available, it is not easy to judge 

 to what extent it is possible to produce muta- 

 tions at desire with his method. Tower has 

 apparently succeeded in producing in various 

 species of Leptinotarsa certain color muta- 

 tions at desire by submitting the beetles, dur- 

 ing the period of the growth of the eggs, to 

 different degrees of temperature and moisture 

 from those in which they usually live. Gager 

 mentions that by treating the pollen or ovaries 

 of Oenothera with radium, some of the new 

 plants were entirely different from the mother 

 plant. Morgan has published the statement 

 that a number of the interesting mutations of 

 Drosophila, which he has recently described, 

 came from a culture which had been treated 

 with radium. 



The following experiments were undertaken 

 for the purpose of forming a conception con- 

 cerning the degree of certainty with which 

 mutations can be produced experimentally. 

 We tried the effects of a constant and com- 

 paratively high temperature, of radium and 

 of Eontgen rays. The stock of Drosophila 

 which we used in these experiments was given 

 us kindly by Dr. Lutz, to whom we wish to 

 express our thanks. 



1. Effects of High Temperature. — Several 

 culture dishes with Drosophila were put into 

 a thermostat, the temperature of which re- 

 mained constant within 1° around 30.5° C. 

 We found that at higher temperatures we lost 

 a large number of cultures. In the fifth gen- 

 eration of files, kept in the thermostat, on 

 February 16, a number of dark flies appeared. 

 They were mated with normal ones of the same 

 culture. Some of these cultures were kept in 

 the thermostat and others were brought into 

 room temperature, to see whether at a lower 

 temperature they would continue to breed 

 true. This has now been the case for five 



