34 



MORPHOLOGY OF GYMNOSPERMS 



"nucellar beak," which is said to "arise from the floor of the pollen 

 chamber," is in reality a core of tissue left intact in the formation of 

 the pollen chamber. An important feature to note in the seeds of 

 this group is that the open tube of the pollen chamber projects a 

 little through the micropyle, so that the passage for the entrance of 

 the pollen grains is not furnished by the micropyle, but by the pro- 

 truding nucellar beak (86, 87). 



Fig. 29. —Lagenosloma ovoidcs: longitudinal section through apex of seed- shown 

 in fig. 28, illustrating an earl)' stage in the formation of the pollen chamber; n, central 

 portion of nucellus which becomes the core shown in fig. 27; «', outer hard part of 

 nucellus; p, beginning of pollen chamber; m, megaspore membrane; i, integument; 

 X36. 



The impression described as Lagenostoma Sindairii (51) shows 

 the same type of seed (fig. 26), so far as external characters are con- 

 cerned, and furthermore it shows its connection with foliage of the 

 Sphenopteris type. 



It is evident that in comparing these seeds with those of living 

 gymnosperms they must be regarded as resembling those of cycads, 

 with decided peculiarities of their own. It is still further evident 

 that such seeds are very far from being primitive in structure, and 

 are no more suggestive of the origin of seeds in general than are the 

 seeds of existing seed plants. 



Physostoma. — Recently Oliver (85) has restored this genus, 

 described first by Williamson (2), but later referred by him (3) to 



