Spermatophytes A ngiosperms 269 



at the top may show the first division, while those at the bottom 

 show the second. Determine the stage by examining a few mother 

 cells before fixing. 



From what has been said, it is evident that longitudinal sections 

 should be cut to show mitosis. Transverse sections should be cut 

 to show the general structure of the anther. It is not necessary to 







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FIG. 94. Lilium candidum: photomicrograph of mitosis in pollen mother cells; 

 in one of the pollen mother cells the twelve chromosomes can be counted; from a prepara- 

 tion by F. L. Pickett. X260. 



cut the stamens into pieces before fixing, since they are easily pene- 

 trated and infiltrated; in later stages the stamens must not be cut 

 into pieces, since the pollen grains are easily washed out. 



The problem of fixing spore mother cells has received much atten- 

 tion. In fixing mother cells and the two mitoses by which spores 

 are formed, investigators have used almost exclusively the chromo- 

 osmo-acetic acid solutions of Flemming, some preferring the 

 weaker solution and some the stronger. These solutions have 

 been used in nearly all of the work of the Bonn (Germany) school. 



