94 GBNEEA or imCERTAIN POSITION [CH. 



In habit Dicranophyllum resembles Lepidodendron ; it is au 

 arborescent plant sparsely and irregularly though sometimes 

 dichotomously branched; the leaves are crowded and spirally 

 disposed, in some species persistent — in the sense in which the 

 leaves of Araucaria are persistent — while in others they probably 

 fell at an earlier stage. The leaves (fig. 671) exhibit a wide range 

 in size, in the amount of lobing and the angle of divergence of the 

 segments; there is no diflerentiation into a lamina and petiole 

 nor are there any short foliage-shoots as in Ginkgo; the whole 

 leaf is represented by a narrow lamina, in some species almost 

 spinous, which consists in the basal portion of a simple linear 

 'stalk' reaching in extreme cases a breadth of about 7 mm., 

 attached by a decurrent base which persists as an elongated cushion 

 closely resembling the leaf-base on some Lycopodiums or the 

 projecting cushions of Picea (cf. fig. 140, Vol. n. p. 94). The 

 cushions are contiguous and cover the surface of a branch as in 

 Lepidodendron, but they are distinguished by the occurrence of 

 the leaf-scar at the apex of the cushion in contrast to its sub- 

 apical position in Lepidodendron. The typical form of the leaf- 

 base is shown in fig. 671, A, but in Dicranophyllum BenecJcianum 

 Sterz. the transversely elongated leaf -scars are almost contiguous 

 as in some species of Sigillaria. At a distance from the base 

 varying in different species the lamina is divided into two, generally 

 equal, branches that diverge at an acute or wide angle, and in 

 most species each arm undergoes one or more bifurcations in a 

 single plane. The whole leaf may reach a length of over 20 cm. 

 In the basal portion of the lamina there are two or more parallel 

 veins, but in branches in which the leaf-scars are well preserved 

 there is only a single vascular-bundle scar indicating a single 

 leaf-trace up to the base of the lamina. Each segment of the 

 leaf has usually two veins and the acutely pointed ultimate 

 segments have a median vein. The so-called secondary or inter- 

 stitial veins are no doubt due to the presence of hypodermal 

 stereome strands. The narrower Dicranophyllum leaves are very 

 similar .to the deeply divided pinnae of Macrozamia heteromera 

 (fig. 671 ; cf. fig. 396, F, Vol. iii. p. 26). The branching of the lamina 

 is generally regular but in several instances the subdivision is 

 irregular (fig. 671, D). On young shoots the leaves may be 



