OF LOWER GREENSAXD PLANTS. 23 



alternating pinnae, each of which has a single midrib or a series 

 of simple veins running parallel in the lamina and unbranched, 

 or with simple, few dichotomising, branches. 



Scale-leaves are also prevalent, and in some cases series of 

 scars of scale-leaves and folitige leaf-bases alternate. 



The sub-class contains two principal orders, the modern 

 Cyeadaceee with relatively simple cones or sporophylls, male 

 and female separate, which are borne externally and apparently 

 terminally on the trunk : and the fossil order Bennettiteae with 

 complex, bi-sporangiate cones borne in large numbers laterally 

 and embedded among the leaf-bases. 



Order BENNETTITEAE. 



The Order is entirely extinct. The trunks, as described for 

 the family, are commonly about 30-60 cm. in height, seldom 

 more than 1 metre. Trunks, as a rule, conical or almost 

 spherical, generally simple ; but in some cases two or three 

 similar short trunks are associated and evidently form a branch- 

 ing individual. The trunk may have a large terminal bud, but 

 this is usually poorly preserved, Kamenta between the leaf- 

 bases are very numerous nmltieeilular scales or hairs. In 

 weathered specimens these tend to form ridges of more resistent 

 tissue round the weathered- out leaf-bases. The fructifications 

 are very numerous, in some cases several hundred per indivi- 

 dual*, and are all in the form of cones with a short central 

 axis, bearing bi-sporangiate lateral appendages and enclosed in 

 sterile scales. The whole cone in each case is deeply embedded 

 among the protecting leaf-bases of the trunk. The seeds, borne 

 singly on special appendages, contain when ripe an embryo 

 which has two cotyledons almost filling up the seed-cavity. 



Genus BENNETTITES, Carruthers. 

 [Trans. Linn. Soc., vol. 26, 1870, pp. 681, 694 et seq.] 



The diagnosis given by Carruthers is as follows : " Trunk 

 ovoid, in transverse section elliptical, covered with the somewhat 



* Thus Wielanrl, 1911. p. 135, describes as many as 500-600 ovulate 

 cones in half -A trunk in one of his new specimens. 



