526 



BOTANY OF THE LIVING PLANT 



The living Gymnosperms may be regarded as the survivors of a 

 large class of Plants of earlier periods, and accordingly their representa- 

 tives appear rather isolated and distinct from one another. They 

 comprise the Cycadales, Ginkgoales, Gnetales, and Coniferales. The 



last is the leading Class of living Gymnosperms, and it includes the 

 greatest number of species. They arc called the Coniferales from the 



A B 



Fig. 414. 



,<4«= mature cone of the Scots Pine, natural size. />', a single scale of th^ cone, 

 seen from above, showing the two ovules, together with the outline of the film of 

 tissue which separates with the ripe seed. Enlarged. (After Le Maout.) 



fruiting body usual for them, which is composed of closely packed 

 hard woody scales, as js well exemplified by the ordinary Fir Cone 

 (Fig. 414, A.) In some, however, a definite woody cone is not formed. 



Cycadales. 



The Cycadales arc represented at the present day by nine genera, and 

 abont 100 species of Fern-like Plants, widely distributed in Tropical and 

 Sub-Tropical regions. These are the relics of a Flora which appears to have 

 reached a climax in numbers and importance in the Oolitic and Cretaceous 

 Periods. In habit they are megaphyllous, often with upright stems, and 

 pinnate or sometimes doubly pinnate leaves. The texture of their leaves is 

 stiff, leathery, and even spinous, and they are constructed on a plan like that 

 of the Marattiaccous Ferns, but specialised for withstanding drought. Their 

 Stems are thick and fleshy, and comparison of their internal structure points 

 again to the Marat tiaceous Ferns, to which some of the related fossils corre- 

 spond in marked degree. 



The Cycads are reproduced by seeds. The ovules (megasporangia) from 

 which they are matured arc borne freely exposed upon the margins of the 

 carpels, or mcgasporophylls : these are often associated in closely packed 



