1929] Babcoch-Clausen: Meiosis in Crepis 405 



In some cases, as for example in many species of Viola, it is impos- 

 sible to stain Carnoy-fixed material with gentian violet. Also it is 

 sometimes better to apply the iodine before the staining, when the 

 objects have been fixed in Carnoy. The iodine seems to have the effect 

 of binding the stain to the tissue. But in many cases it binds the 

 stain too much and it is impossible to get it out of the plasm again. 

 The use of iodine and gentian violet can be varied in many ways. 

 The method is also very dependent upon the fixative used. Neither 

 in Viola nor in Crepis was any case found where iodine-gentian violet 

 failed on material fixed in Navashin's or in Carnoy-Navashin 's fluid. 



In order to try the effect of acetic acid, some slides were treated 

 for half an hour with 45 per cent acetic acid. The pollen mother cells 

 swelled somewhat. The acetic acid did not destroy the gentian violet 

 applied for staining but the differentiation was not so good as in the 

 slides not treated with acetic acid. Some sectioned slides were stained 

 with iron-acetocarmine but the effect was much inferior to that of 

 iron-acetocarmine applied on smears. There was too little differentia- 

 tion between chromosomes and plasm. 



The ideal method for Crepis seems to be to have root tips fixed in 

 Navashin's fluid and stained with Heidenhain's haemotoxylin (Nava- 

 shin 1925, 1926), to have younger buds fixed in Carnoy-Navashin and 

 stained with iodine-gentian violet-orange G for examination of the 

 prophases, the heterotypic, and the homotypic divisions, and to have 

 older buds fixed in Carnoy for examination of tetrad stages in iron- 

 acetocarmine. 



MEIOSIS IN CREPIS ASPERA L. AND C. BURSIFOLIA L. 



The chromosome numbers are w=4 in hoth Crepis aspera (Marchal 



1920; Mann 1925) and C. hursifoHa (Mann 1925). While there is 



not much difference in size between the aspera chromosomes, Mann 



found one chromosome in hursifoHa considerably shorter than the 



others. She gives the comparative lengths as follows (determined on 



chromosomes in root-tip cells) : 



C. aspera 23.9 21.5 19.7 17.5 



C. lursifolia 24.3 22.0 19.5 12.7 



Except for the shortest one, the chromosomes of the two species 

 apparently correspond in length. 



During the stages of meiotic division the small chromosome pair 

 of C. hursifoHa can be recognized (pi. 58, figs. 12-15; pi. 59, figs. 



