44 



MORPHOLOGY OF GYMNOSPERMS 



sperms the nucellus and integument are entirely free in the early 

 stages of the ovule; and the later growth of the ovule being in the 



chalazal region, the 

 free integument and 

 nucellus are carried 

 to the tip. This 

 seems to have taken 

 place in Lagenos- 

 toma, and not in 

 Stephanospermum; 

 but whether this 

 latter character rep- 

 resents an ancient 

 feature of ovules in 

 general or not can 

 be determined only 

 by a much larger 

 knowledge of the 

 structure of the 

 older paleozoic 

 seeds. 



Oliver has 

 shown (46) also 

 that the permo- 

 carboniferous seed 

 genera Trigone- 

 carpum (almost 

 certainly to be re- 

 ferred to theMedul- 

 losineae among 

 Cycadofilicales) and 

 Polylophospermum 

 are of the Stephano- 

 spermum type (with 

 broad pollen chambers, nucellar tracheal mantle, and difierentiated 

 testa), the former being a three-ridged seed, the latter a hexagonal 

 one. Besides these variations in the form of the seed, other varia- 



FlG. 46. — Trigonocarpum ParkinsonU: diagrammatic 

 median longitudinal section in the plane of the "wing"; 

 for lettering see fig. 48. 



