n6 



ANCIENT PLANTS 



leaves belonged to the stem, and so on. By a series of 

 lengthy and painstaking investigations all the parts of 

 the plant now called Lyginodendron have been brought 

 together, and the impressions of its leaves have been 

 connected with it, these being of the fernlike type so 

 long called Sphenopteris, illustrated in fig. ']']. 



The anatomy of the main stem is very suggestive 

 of that of a Cycad. The zones of secondary wood are 



Fig. 78A. — Diagram of the J ransverse Section of Stem oi \h& Lyginodendron 



p, Pitli ; P, primary wood groups; w, secondary wood ; Lt, leaf -trace; s, sclerized 

 bands in tlie cortex ; s, longitudinal view of wood elements to show the rows of 

 bordered pits. 



loosely built, the quantity of soft tissue between the 

 radiating bands of wood, and the size of the pith being 

 large, while from the main axis double strands of wood 

 run out to the leaf base. The primary bundles, how- 

 ever, are not like those of a Cycad stem, but have groups 

 of centripetal wood within the protoxylem, and thus 

 resemble the primary bundles of Poroxylon (see p. 97), 

 which are more primitive in this respect than those of 

 the Cycads. 



