88 CARNEGIE INSTITUTION OF WASHINGTON. 



the number of chromosomes in the nucleus is permanently doubled. Further- 

 more, the resulting new form meets the above-named criteria of a species. 



Admitting this to be a real method of species origin, the question of the 

 origin of species is far from being answered. But our experience so far justi- 

 fies us in concluding that the question of the origin of species is at basis that 

 of the origin of changes in the chromosomes; and the question of evolution is, 

 in part, that of the evolution of the chromosome complex and, in part, that 

 of adjustment to environment, in which the environment acts as the ruthless 

 selector. 



Even had we learned the various internal and external influences that 

 control chromosomal changes we should be far from having a complete 

 insight into genetics. The question would still be urgent, How do the deter- 

 miners or genes of the chromosomes work out their destiny in particular 

 somatic traits? Into this matter we are gaining some insight by studies 

 on the role of hormones in development and, indeed, by the various analyses 

 of the genetic elements of adult traits. 



Twenty years have passed since this Department or its predecessor (that 

 of Experimental Evolution) was founded. One of the appointees of the first 

 year was a cytologist, a recognition of the importance of the cytological basis 

 of genetics. During this period, which nearly coincides with that of the 

 modern development of genetics, the chromosome has come ever more and 

 more into the foreground. The next new developments are, doubtless, 

 those of biological physical chemistry, a discipline in which little research 

 has yet been done. But until research is pushed in this field we shall not 

 know the relation between the chromosomes and the processes of general 

 growth and differentiation, which are the essence of that development of 

 which heredity is the control. 



DETAILED REPORTS ON CURRENT INVESTIGATIONS. 



INTERCHROMOSOMAL MUTATION. 



The reports of the past few years have recorded in detail the rise and 

 progress of our research on the relation between the extraordinary irregu- 

 larity of the karyokinetic phenomena in the formation of gametes in the 

 jimson weed (Datura) and the equally rare variability in the somas of these 

 plants. To learn all of the somatic changes induced by the chromosomal 

 irregularities requires the cooperation of persons with special technical 

 knowledge in different fields, and this cooperation we have been able to 

 obtain from university men who have come to us for the summer months. 

 The resident group in these experiments is composed of Dr. A. F. Blakeslee, 

 who has directed them from the beginning; Dr. John Belling, who is making 

 cytological studies and has had the temporary assistance of Misses Elizabeth 

 Lord and Rachel Haynes; Mr. M. E. Farnham and his successor, Mr. 

 Gordon Morrison, who have had immediate charge of most of the work in 

 the greenhouse and field. The visiting collaborators have again been Pro- 

 fessor E. W. Sinnott, of the Connecticut Agricultural College at Storrs, who 

 has been studying the anatomy and histology of the mutants; Professor 

 John T. Buchholz, of the University of Arkansas, who has continued his 

 studies of the differences in the growth of the pollen-tubes of different 

 daturas in the pistils of Datura mutants; and Mr. J. L. Cartledge, of the 

 University of Pittsburgh, who has been engaged in pollen counts and assist- 



