328 



METHODS IN PLANT HISTOLOGY 



10 per cent glycerin and follow the Venetian turpentine method. 

 When the turpentine becomes thick enough for mounting, tease the 

 pollen tubes from the nucellus and mount with pieces of cover glass 



Fig. 113. — Ceratozamia mexicana: photomicrograph of a longitudinal section of a sperm, show- 

 ing the very large nucleus, thin sheath of protoplasm which is thicker at the apical end, and blepharo- 

 plast cut across in various places and bearing numerous cilia. At this stage, the sperm is swimming 

 in the pollen tube. Cramer contrast plate. Negative by Miss Ethel Thomas. X506. 



under the cover to prevent crushing. Iron-alum haematoxylin, which 

 is so satisfactory for staining sections of sperms, is the most unsatisfac- 

 tory stain we have tried for staining the cycad pollen-tube structures 

 whole. 



