No. 632] SHORTER ARTICLES AND DISCUSSION 271 



yet it can not be denied that many biologists are not yet com- 

 mitted to the acceptance of these conclusions as of general ap- 

 plication. It is obvious that extensive corroborative evidence, 

 derived from other genera of animals and plants, would be of 

 paramount value in firmly establishing these far-reaching con- 

 clusions. It, therefore, becomes one, who allies himself with 

 those biologists who believe in the present importance and future 

 promise of this collection of genetic evidence, derived as it is, 

 almost entirely from a single species of insects, to consider most 

 carefully the selection of other material with which to test the 

 various hypotheses that have been proposed in order to interpret 

 the great mass of drosophila data consistently. 



It is encouraging to note the energetic efforts of a number of 

 investigators to obtain a corresponding collection of data from 

 other species of Drosophila, As yet, however, little more than 

 a beginning has been made, particularly with the genetic inves- 

 tigations on these species, because it is necessary first to find 

 the comparatively rare mutant individuals with which to ex- 

 periment. No other genus of animals thus far reported upon 

 possesses so many features favorable to genetic study as does 

 Drosophila, although it is probable that other of the lower ani- 

 mal groups will in time furnish material just as valuable. In 

 plants, the only species in which genetic analysis has proceeded 

 far enough to establish the identity of a considerable number of 

 hereditary factors or genes, are the garden pea, sweet pea, snap- 

 dragon, maize, barley and wheat. In most of these and in some 

 other plants evidence of linkage of characters in inheritance has 

 been obtained, but in none has the number of linked groups been 

 shown to correspond with the number of chromosomes in the 

 germ cell and because of the relatively large number of chromo- 

 somes in these species it will probably be some time before any 

 considerable body of corroborative evidence can be accumulated 

 from them. 



In addition to a low chromosome number there are several 

 other desiderata which the ideal form for genetic investigations 

 should possess. It must display numerous germinal variations. 

 It must be prolific and easily reared. It should have a short life 

 cycle so as to permit of the maximum number of generations 

 within a given time. Furthermore, in the case of a plant, it 

 should be self-fertile, so as to permit of establishing pure lines; 

 it should be easily hybridized ; and it should flourish when grown 

 under glass. 



