44 STUDIES IN FOSSIL BOTANY 



appendages in which the typical Astromyelon structure 

 is evident. 1 This evidence proved quite conclusively 

 that Astromyelon was only an appendage of the stem 

 of Calamites. Since then the connection between the 

 two organs has also been clearly demonstrated in 

 various specimens from the English Coal-measures. 



The relation between the roots and the stem has 

 recently been fully investigated by Mr. Maslen, 2 who 

 finds that the roots, like the branches, were commonly 

 inserted on the node, between two of the outgoing leaf- 

 traces (cf. Fig. 9) ; the roots, however, arise on a level 

 with the leaf-traces, and not above them, and pursue 

 a somewhat downwardly directed course in passing 

 through the wood of the main axis. 



The question whether these appendages were roots 

 or branches had to be decided from the anatomy. In 

 the first place, as already mentioned, the primary 

 xylem was centripetally developed. On the inner side 

 of each woody wedge we find in transverse section a 

 little triangular group of tracheae, and this triangular 

 group has always the smaller elements towards the 

 exterior (see Fig. 15, x x ). Radial sections prove that 

 these external elements of the primary wood are spiral 

 tracheae, and thus the position of the protoxylem is 

 shown to be that characteristic of roots. 



Another point of crucial importance is the arrange- 

 ment of the primary xylem and phloem groups ; it is 

 not often that such a point as this can be demonstrated 

 in a fossil. We were able, in one or two favourable 



1 Flore fossile du Bassin houiller cCAutun et dEpinac, Part ii. p. 106, 

 Plate lii. etc. 



2 A. J. Maslen, " Relation of Root to Stem in Calamites," Annals oj 

 Botany, vol. xix. 1905, p. 61. 



