ROOTS OF CALAMARIEAE 



45 



cases, to trace the centripetal strands of xylem in a 

 young root, and to find, alternating with them, groups 

 of delicate tissue, which could only be interpreted as 

 primary phloem. Hence, in this respect also, the 

 structure proves to be that of a typical root. 



We further found that the bases of branches of 

 Astromyelon are surrounded by a distinct cortex of their 

 own, as they traverse the outer tissues of the parent 

 organ. Hence they 

 must have been endo- 

 genous in origin, thus 

 agreeing with rootlets. 

 Another important 

 point is the entire 

 absence of anything 

 like nodes. 



There is thus, on 

 the whole of the evi- 

 dence, no room for 

 doubt that the old genus 

 " Astromyelon " simply 

 represents the roots 

 and rootlets of Cata- 

 mites} Other allied forms appear to stand in a similar 

 relation to Archaeocalamites and Calamodendron. 



The endodermis was evidently double, as in the 

 roots of recent Horsetails ; this is well shown in the 

 small tetrarch rootlet represented in Fig. 16. The 

 large intercellular spaces of the cortex were no doubt 

 an adaptation for growth under water, or in wet mud. 



1 Williamson and Scott, "Further Observations, etc.," Part ii. The 

 Roots of Catamites, Phil. Trans, vol. 186, B, 1895. 



Fig. 16. — Catamites, sp. Transverse section 01 

 small tetrarch rootlet, showing wood (x), with 

 slight secondary growth, double endodermis, 

 lacunar cortex (c), and thickened exodermis. 

 X 25. From a photog'aph. Phil. Trans. 

 W. and S. Will. Coll. 1S90, A. 



