i6o ANCIENT PLANTS 



selves were more like those of Lepidodendron. In fig. 

 1 1 8 is a diagram of a trilobed bract with its three 

 attached sporophylls. Round the axis were very numer- 

 ous whorls of such bracts, and as the cone was large 

 there were enormous numbers of spore sacs. 



A point of interest is the character of the wood of 

 the main axis, which is similar to that of Lepidoden- 

 dron in many respects, being a ring of centripetally 

 developed wood with twelve projecting external points 

 of protoxylem. 



This cone ^ is the most complex fructification of any 

 of the known Pteridophytes, whether living or fossil, 

 which alone ensures it a special importance, though for 

 our purpose the mixed affinities it shows are of greater 

 interest. 



To mention some of its characters: — The individual 

 segments of the sporophylls, each bearing four sporangia, 

 are comparable with those of Calamites, while the indi- 

 vidual sporangia and the length of the sporophyll stalk 

 are similar in appearance to those oi Lepidodendron. The 

 wood of the main axis also resembles that of a typical 

 Lepidodendron. The way the vascular bundles of the 

 bract pass out from the axis, and the way the stalks 

 bearing the sporangia are attached to the sterile part 

 of the bracts, are like the corresponding features in 

 Sphenophylhun, and still more like Bowmanites. 



Many other points of comparison are to be found 

 in these plants, but without going into further detail 

 enough has been indicated to support the conclusion 

 that CheirostrobiLS is a very important clue to the 

 affinities of the Sphenophyllales and early Pteridophytes. 

 It is indeed considered to have belonged to an ancient 

 stock of plant's, from which the Equisetaceae, and Spheno- 

 phylla, and possibly also the Lycopods all sprang. 



Sphenophyllum, Bowmanites, and Cheirostrobus, a 

 series of forms that became extinct in the Palseozoic, 

 remote in their structure from any living types, whose 



' For fuller description of this interesting cone, see Scott's Studies, p. i\/^et seq. 



