Darling: Sex in dioecious plants 197 



^ 



Punnett, R. C, & Bateson, W. '08. The heredity of sex. Science 

 II. 27: 785. 1908. 



Stevens, N. M. '06. Studies in spermatogenesis — 11. A compara- 

 tive study of the heterochromosomes in certain species of Coleoptera, 

 Hemiptera, and Lepidoptera with special reference to sex determina- 

 tion. Carnegie Inst,^ Washington, Pub. 36^ 1906. 



Strasburger, E. '00. Versuche mit diocischen Pflanzen in Riicksicht 

 auf Geschlechtsverteilung. Biol. Centralbl. 20: 657. 1900. 



. ^oB* Chromosomenzahlen, Plasmastrukturen, Vererbungstrager, 



und Reduktionsteilung. Jahrb. Wiss. Bot. 45: 479, 1908. 



Van Wisselingh, C. '98. Ueber den Nucleolus von ^/r^^'m. Bot, 



Zeit. 56\- 195. 1898. 



Wager, H, '04. The nucleolus and nuclear division in the root-apex 



of Phaseoliis. Ann. Bot. 18 : 29. 1904. 



Wilson, E. B. '00. The cell in development and inheritance. New 

 York, 1900. 



. 'q6. Studies on chromosomes, III. The sexual differences of 



1 



chromosome groups in Hemiptera, with some considerations on the 

 determination and inheritance of sex. Tour. Exp. Z06I. 3:1. 1906. 



— . '09a. Studies on chromosomes, IV. The '' accessory '* 

 chromosome in Syromastes and Pyrrochorisy with a comparative 

 review of the types of sexual differences of the chromosome groups. 

 Jour. Exp. Z06I. 4: 69. 1909. 



— . '09b. Recent researches on the determination and heredity of 

 sex. Science 11. 29: 53. 1909. 



Cxplanatfoti of plates 12-14 



All figures were made by means of a camera lucida with Spencer 1,5 mm. objec- 

 tive and Leitz compens, ocular 12. The original drawings were reduced one third; 



000 



Plate 12 



1. Mother cell in early growth period with single, spherical nucleolus and non- 

 staining bodies on linin, 



2. Mother cell showing chromatin body just appearing on the nucleolus. 



3. The nucleus slightly larger, the chromatin body farther out from nucleolus. 



4. The chromatin body nearly free, attached by a thread. 



5. Chromatin body free, a second appearing. 



6. The first chromatin body attached to the linin and beginning to lose its chro- 

 matin. The second nearly free* 



7. Several chromatin bodies diffusing out on the linin, others appearing. The 



thread becoming more apparent. 



