194 LYCOPODIALES [CH. 



tion of Scott's paper our knowledge of this type has been 

 extended by Miss Berridge^ and by Prof. Lang". 



The axis of the strobilus has a stele characterised by a 

 pith of elongated elements, most of which have thin walls; 

 the xylem cylinder possesses about twenty protoxylem strands 

 forming more or less prominent exarch ridges. The cortex 

 exhibits a differentiation comparable with that in the shoots of 

 Lepidodendron. The sporophylls are arranged in alternating 

 verticils, each whorl consisting of ten members: the narrow 

 horizontal pedicel of a sporophyll, containing a single vascular 

 bundle, as shown in fig. 192, is expanded distally into a 

 prominent upper lobe bearing a cushion of small and delicate 

 cells, to which the sporangium is attached, and prolonged obliquely 

 upwards as a free leaf-like lamina. The lower blunt prolonga- 

 tion of the sporophylls appears to form a thick dorsal lobe, but, 

 as Lang has pointed out, it is highly probable that the present 

 form of the dorsal lobe is of secondary origin, and is " due to the 

 disappearance of a mucilage cavity from a large sporophyll 

 baseV As Miss Berridge remarks, the vascular bundle of the 

 sporophyll does not give off a branch to the ventral lobe and 

 sporangium. In attachment, in shape, and in the structure of 

 the wall the sporangia differ markedly from those of Lepidostrohi. 

 The spores, which also constitute a characteristic feature of 

 the genus, have a maximum diameter of 0"14 mm. ; they are 

 described as oblate spheroids with a broad hollow wing running 

 round the equator (fig. 192) comparable with the air-sacs of the 

 pollen of Pinus. Scott points out that the spores of Spencerites 

 are intermediate in size between the microspores of Lepidoden- 

 dron and the megaspores of Lycopodium; it is difficult therefore 

 to decide to which category they should be referred. Spencerites 

 is clearly distinct from Lepidostrobus ; the absence of a ligule, 

 the manner of attachment of the sporangia, and the form and 

 size of the spores, are characteristic features. 



A comparison of Spencerites with the strobili of Lycopodium 

 cernuum (figs. 123, 126—129) has recently been made by Lang, 

 who draws attention to the striking agreement as regards general 

 plan and even detailed structural features between the Palaeozoic 



1 Berridge (05). ^ L^ng (qq). . ^^ng (08) p. 364. 



