204 



JNIORI'IIOLOGY 



veins that branch dichotomously, except in certain forms with \cry 

 narrow leaves. In some forms the leaves are short and obovate, sug- 

 gesting those of Gink- 

 goales. The structure of 

 the leaves is like those 

 of the cycads, \\ith the 

 very characteristic meso- 

 phyll (see p. 193). In 

 form, therefore, the leaves 

 in general resemble those 

 of the conifers ; but in 

 structure they resemble 

 tliose of the cycad line. 



Strobili. — The strobih 

 are small and monospo- 

 rangiate, both kinds of 

 stroliili usually occurring 

 on the same plant (monoe- 

 cious), characters which 

 belong to the conifers. 

 Thev occur in clusters 

 on lateral branches dig. 

 461), and both kinds are 

 sheathed by bracts. 



SUiDiinate. — The stam- 

 inate strobilus is made u]j 

 of spirally arranged sterile 

 bracts, among whicli the 

 stamens occur, either soli- 

 tary or groupied near the 

 apex (fig. 462). Each 



Fig. 4fjr. — Rc-sto.^atlon of DorvrorJaiUs, one of ^ . i i ^ n 



^,., ,. ..',. ,, . Stamen is a slender stalk 



the Cordaitales, showmy the branching' habit, the 



simple, elongated, parallel-veined leaves, and the bearing a terminal cluster 



clusters of strobili borne on lateral branches. — .\fter ,,f three to si .X erect SI to- 



rangia with longitudinal 

 dehiscence. It is only among the Cycadofilicales that such terminal 

 and erect microsporangia are found (cu])ule tyiic, see p. 184). 



Oviihilc. — The o\-iilatc strobilus i- made up of conspicuous over- 

 lapping brads, in \\hose axils short branches appear, each of which 



