I04 



ANCIENT PLANTS 



They were widely spread in Lower Mesozoic times, the 

 plants being preserved as casts, impressions, and with 

 structure in great numbers. The btilk of the described 

 structural specimens have been obtained from the rocl<s 

 of England, France, Italy, and America, although leaf 

 impressions are almost universally known. The genus 

 Williamsonia belongs to this family, and is one of the 

 best known of Mesozoic plant impressions. 



Externally the Bennettiteae were 

 identical in appearance with stumpy 

 Cycads, and their leaves it is which 

 gave rise to the surmise, so long pre- 

 valent, that the Lower Mesozoic was 

 the " Age of Cycads ", just as it was 

 the Pteridosperm leaves that gave the 

 Palaeozoic the credit of being the 

 "Age of Ferns ". In the anatomy of 

 both stem and leaf, also, the characters 

 are entirely Cycadean; the outgoing 

 leaf trace is indeed simpler in its 

 course than that of the Cycads. 



The fructifications, however, differ 

 fundamentally from those of the Cy- 

 cads, as indeed they do from those of 

 any known family. They took the 

 form of compact cones, which occurred 

 in very large numbers in the mature 

 plants hidden by the leaf bases. In Williamsonia, of 

 which we know much less detail, the fructifications stood 

 away from the main axis on long pedicels. 



In Bennettites the cones were composed of series of 

 sheathing scales surrounding a short conical axis on 

 which stood thin radiating stalks, each bearing a seed. 

 Between them were long-stalked sterile scales with ex- 

 panded ends. A part of a cone is illustrated diagram- 

 matically in fig. 71. The whole had much the appear- 

 of a complex fruit. In some specimens these 



Fig. 71. — Half of a Lon- 

 gitudinal Section through 

 a Mature Cone of Bennet- 

 tites 



A, Short conical axis; 

 s, enclosing bracts ; s, 

 seeds ; sc, sterile scales 

 between the seeds. 



ance 



features alone are present in the cones, but in younger 



