340 



METHODS IN PLANT HISTOLOGY 



prothallial cells cannot always be detected at this stage, and there may 

 be some doubt as to whether two such cells are always present. The 

 division of the lenticular cell into "stalk cell" and "body cell," and also 

 the division of the body cell into the two male cells, must be looked 

 for in sections of the nucellus of the ovule. As stated before, the dates 

 are for Pinus laricio in the vicinity of Chicago. In P. banksiana, 



Fig. 118. — Abies balsamea: photomicrograph of pollen; one complete section showing two pro- 

 thallial cells, the stalk cell, generation cell, and tube cell with starch grains. Fixed and cut while 

 still within the microsporangium. Stained in safranin and gentian violet. Eastman Commercial 

 Ortho film, Wratten B filter (green); Spencer 4-mm. objective, N.A. 0.66; ocular X6; arc light; ex- 

 posure, 6 seconds. Preparation by Dr. A. H. Hutchinson, negative by Dr. P. J. Sedgwick. X784. 



stages come about 2-3 weeks earher. In pines in the Gulf states, the 

 dates are still earlier. No pines are native in the Southern Hemisphere, 

 but in cultivated specimens, which are very common, the dates are 

 about 6 months from the Northern Hemisphere dates. 



Abies balsamea is a better type for illustrating spermatogenesis, 

 since the pollen mother-cells and the pollen grains are much larger 

 and the division of the generative cell into the "stalk" and "body" 

 cells takes place before the pollen is shed (Fig. 118). 



Araucaria and Agathis are the best forms for illustrating numer- 

 ous prothallial cells. Podocarpus and Taxodium are also good. Thuja 



