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MORPHOLOGY OF SPBRMATOPHYTES 



acteristic of Cycads and Ginkgo, and the extinct groups ; nor is 

 there any distinctly organized pollen chamber, although we 

 have observed in Pinus that the nucellus breaks down at the 

 apex, so that the pollen grains lie in a cuplike depression. 



Although the primary sporogenous cells are cut off by the 

 hypodermal layer they are not distinguishable from the neigh- 

 boring cells until they have become deeply placed in the chalazal 



Fig. 63. — Pinus Laricio, longitudinal section of megasporangia June Ist, with mega- 

 spore mother cell in the center, surrounded by a region of more or less modified cells ; 

 the nucleus of the mother cell is in the prophase of the reduction division ; x 500. 



region of the nucellus, and even then there is no differentiation 

 to attract attention until a mother cell begins to enlarge. This 

 tardy differentiation of the sporogenous cells in appearance was 

 remarked by Strasburger in the case of Taxus, and we have 

 found it to be strikingly true in Pinus. Apparently the pri- 

 mary sporogenous cells do not divide, but one or more of them 

 pass over directly into mother cells. Several mother cells have 

 been observed to begin to enlarge in Taxus and in Sequoia, but 



