306 



is less precision in the dilTerent slages Ihan in the helerotype. The 

 paiiners of the bivalenls are segmentet! and tlieir halves pass to 

 the poles. The same behaviour is shown, in many cases, by the 

 descendants of the singles too. In the telophase a new elimination 

 of the last mentioned chromosome elements takes place, the four 

 ordinary microspores (containing the descendanls of the gemini 



Fig. 2. a. R. (Coriifoliac) *solanifolia Matss. Diakinesis showing 7 bivalent and 

 21 unpaired chromosomes. b. R. glnfinosa Sibth. & Sm. ^libanotica Boiss. Meta" 

 phase showing 7 Ijivalents and 28 singles in the same plane. c. R. (Tomentosae) 

 *subcrisfata Schz. Interkinesis after the heterotypic division showing two great and 

 some small nuclei. — Same niagnification as in the first plate. 



thus obtaining only a few or sometimes none of them. In that 

 waj% the chromosome nnmber of these pollen grains will be rather 

 small, sometimes only 7. All the olher microspores — there arises 

 a great number of Ihem from each pollen mother cell — contain 

 only descendants from the univalent chromosomes, and their chro- 

 mosome number then oflen will be slill smaller. 



13. Some of the microspores, probably those containing the 

 descendants of the bivalents, develop into pollen grains and can 



