544 



BOTANY 



PART II 



intermediate links supplied by the latter group the correspondence 

 with the life-history of the Archegoniatae would not be so clearly 

 recognisable. 



These conclusions are confirmed by the evidence afforded by 

 Palaeobotany. Gymnosperms or forms resembling them are found 

 along with what appear to be intermediate forms between the Gymno- 

 sperms and the Pteridophyta in the fossiliferous rocks of the Devonian, 

 Carboniferous, and Permian formations. The Angiosperms are, on 

 the other hand, first known from the Cretaceous formation. 



Morphology and Ecology of the Flower ( 3 ) 



1. Morphology. The flowers of the Gymnosperms are all 

 unisexual and diclinous. The macrosporophylls form the female, the 



B 



N^V; 



/ 



A 



D 



FIG. 510. Pin-us montana. A, Longitudinal section of a ripe male flower (x 10). B, Longitudinal 

 section of a single stamen ( x 20). C, Transverse section of a stamen ( x 27). D, A ripe pollen 

 grain of Pinus sylvestris ( x 400). (After STRASBURGER.) 



microsporophylls the male flowers. The two sexes are found either 

 on the same individual (MONOECIOUS), or each plant bears either male 

 or female flowers (DIOECIOUS). Leaves forming an envelope around 

 the group of sporophylls are only found in a few flowers of the 

 Gymriospermae (Gnetaceae). 



The MALE FLOWERS are shoots of limited length, the axis of which 

 bears the closely crowded and usually spirally arranged sporophylls. 

 The scales which invested the flower in the bud often persist at the 



