No. 556] DEVELOPMENT IN NICOTIAN A 



219 



together, as in certain metaphases, is safranin, magdala 

 red and azure II. Large quantities of the fresh mate- 

 rial of the anthers in various stages of maturity were 

 stained with methyl green and microscopically exam- 

 ined. In most cases one anther of a bud to be fixed was 

 inspected in this manner. This precaution was neces- 

 sary as a check on the occurrence of artifacts from 

 fixation. 



Briefly, conditions in the normal Cuban variety (402) 

 are as follows. The ordinary maturation processes are 

 those cytologists have so often described for plants, and 

 need no recapitulation here. The spireme in prophase 

 is single and, just preceding diakinesis, breaks up into 

 segments which take the form of twisted and horseshoe- 

 shaped loops. The latter resemble Davis's figures for 

 0. grandiflora 22 Each loop consists of two spireme seg- 

 ments joined at one end, which in the later heterotypic 

 phases separate and go to opposite poles. Each seg- 

 ment is interpreted as a somatic chromosome, and the 

 members of a pair are homologues. The other phases 

 present nothing peculiar. The homotypic chromosomes 

 appear as entities first in very late anaphase of the first 

 division. The reduced chromosome number, as deter- 

 mined by very numerous counts of heterotypic meta- 

 phases and anaphases, and homotypic telophases is 24, the 

 2n being 48. The somatic number (2n) was determined 

 by adding together the homotypic telophase chromo- 

 somes of a tetrad and dividing the entire number by two. 

 Polar views of the metaphase of the first division in sec- 

 tions of 10fi have repeatedly shown the 24 gemini, each 

 geminal chromosome consisting of a diakinetic pair. 

 Variation of chromosome number in these normal (402) 

 anthers is very rarely, if ever, to be found. None was 

 found in the present investigation. Irregular divisions 

 are not common, although occasionally one sees lagging 

 chromosomes. Usually the phases of a single pollen sac 



" Davis, B. M., "Cytological Studies on (Enothera. I. Pollen Develop- 

 ment of (Enothera grandiflora," Ann. Bot., 23: 551-571, PL XLI, Figs. 31, 

 34, 36, 1909. 



