37° 



STUDIES IN FOSSIL BOTANY 



filled by a small-celled secretory tissue (Fig. 136). In 

 certain conditions the glandular tissue has broken down 

 and the head is left empty (Fig. 146). 



We haye so. far described 

 the ordinary structure of the 

 Lyginodendron stem, such as is 

 common to the great majority 

 of the specimens. Sometimes 

 quite young stems are met 

 with, with little or no second- 

 ary growth ; one of these is 

 represented, in transverse sec- 

 tion, in Fig. 135, at a stage 

 when the secondary wood (.t 2 ) 

 was still quite thin. Such 

 specimens show very clearly 

 the identity of the leaf-traces 

 (/./.) with the strands (.r) sur- 

 rounding the pith. At this 

 stage, the outer cortex con- 

 tains only narrow bands of 

 parenchyma ; evidently this 

 tissue increased by dilatation 

 as the stem enlarged in girth. 

 In some cases small stems 

 arc found which are not 

 merely young, but really have 

 a different structure from the 

 usual kind. Some of these little stems have a very 

 small pith, surrounded by a more or less continuous 

 ring of primary xylem, instead of by separate bundles. 

 These specimens may very likely be the stems of 



";. 136. — Lyginodetidi'on aldham- 

 ium. Vegetative gland, showing 

 well - preserved secretory tissue 

 filling the head. The depression 

 on the right of the stalk is a 

 stoma. X about 60. S. Coll. 447. 

 From a photograph hy Mr. L. A. 

 Hoodie, F.L.S. (Phil. Trans. 

 Oliver and Scott.) 



