PAST HISTORIES OF PLANT FAMILIES 



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their nature was partly recognized from it alone, though 

 at that time they were supposed to have only fernlike 

 spores. 



The very numerous impressions of their fernlike 

 foliage from the Palaeozoic rocks indicate that the plants 

 which bore such leaves must have existed at that time 

 in great quantity. They must have been, in fact, one 

 of the dominant types of the vegetation of the period. 

 The recent discovery that so large a proportion of them 

 were not ferns, but were seed-bearing plants, alters the 

 long-established belief that the ferns reached their high- 

 water mark of prosperity in the Coal Measure period. 

 Indeed, the fossils of this age which remain undoubtedly 

 true ferns are far from numerous. It is the seed-bearing 

 Pteridosperms which had their day in Palaeozoic times. 

 Whether they led directly on to the Cycads is as yet 

 uncertain, the probability being rather that they and the 

 Cycads sprang from a common stock which had in some 

 measure the tendencies of both groups. 



That the Pteridosperms in themselves combined 

 many of the most important features of both Ferns and 

 Gymnosperms is illustrated in the account of them given 

 above, which may be summarized as follows: 



SALIENT CHARACTERS OF THE PTERIDOSPERMS 



Gymnospermic 

 Secondary thickening of root. 



Pits on tracheae of primary wood. 

 Secondary thickening of stem. 

 Double leaf trace. 



General organization of the seed. 



Fernlike 

 Primary structure of root. 



In Heterangium and Medullosa the 

 solid centripetal primary wood 

 of stele. 



Fernlike stele in petiole. 

 Fernlike leaves. 

 Sporangia pollen-sac-like. 

 Reproductive organs borne directly 

 on ordinary foliage leaves. 



