544 STUDIES IN FOSSIL BOTANY 



is more developed (Fig. 195, C); grains, which were 

 found lying free in the matrix, were in an intermediate 

 condition ; M. Renault drew the conclusion, that the 

 pollen-grains continued to grow after their discharge 

 from the anther, and more especially after their entrance 

 into the pollen-chamber. 



The cells within the pollen-grain of Cordaites are 

 more numerous than in most recent Gymnosperms ; in 

 the pollen-tube of Microcycas, however, described by 

 Caldwell, 1 sixteen spermatozoids are produced, while in 

 that of Araucaria the number of nuclei present ranges 

 from about twenty to forty-four. 2 In the pollen-grains 

 of Cordaites, as M. Renault pointed out, the cells appear 

 to have been all of one kind. That this structure, 

 whether it be regarded as a prothallus or as an antheri- 

 dium, should have been more developed in primaeval 

 seed-plants than is usual in those of our day, is quite 

 what we should expect, from our knowledge of the 

 conditions in the heterosporous Cryptogams. 3 



Pollen-grains have now been observed, in a number 

 of instances, within the pollen-chambers of Pteridosper- 

 mous and Gymnospermous seeds of the Carboniferous 

 period. There appears to be little or no evidence at 

 present for the formation of pollen-tubes, though the 

 preservation is sometimes good enough for even so 

 delicate a structure to have been detected. It is prob- 

 able that such pollen-grains as those of Cordaites or 

 Stephanospermum may have been a stage nearer the 

 Cryptogamic microspore than those of Cycas or Ginkgo, 



1 "Microcycas calocoma," Bot. Gazette, vol. xliv. 1907, p. 118. 



2 Lopriore, " Uber die Vielkernigkeit der Pollenkorner von Araucaria 

 Bidwillii," Ber. d. Deutsch. Bot. Gesellschaft. vol. xxiii. 1905, p. 335. 



3 See the account of Stephanospermum above, p. 456. 



