THE STEM OF CALAMITES 



23 



transverse section of a stem, the canals are not perfectly 

 empty, but that they contain minute rings adhering to 

 their edges, as indicated in Fig. 4. This suggests very 

 strongly the position of the annular and spiral tracheides 



fix 



sc. 



in Equisetum, which are 

 often found within the 

 carinal canal. To determine 

 the true state of the case, 

 however, a very detailed 

 examination was necessary. 

 There are now many sec- 

 tions showing these canals 

 quite clearly, and proving 

 that they contain the first- 

 formed woody elements, or 

 protoxylem, of the vascular 

 bundles. 



Fig. 6 represents a radial 

 section passing through the 

 canal of one of the bundles. 

 On the inner side of the 

 canal is pith ; on the outer 

 side wood. We notice that 

 the canal is to a great extent 

 occupied by the disorganised tracheae. It is a point 

 of some importance that the disorganisation is found 

 to be greatest on the inner side of the canal, while, as 

 we approach its outer edge, the tracheae become more 

 continuous. We know that the disorganisation of the 

 tracheae is constantly greatest in that part of the 

 primary wood which is differentiated before the growth 

 in length is completed. Hence wc may infer that the 



Sc 



Fig. 6. — Catamites, sp. Part of radial 

 section through primary wood. J>x, 

 disorganised spiral and annular 

 tracheides in the canal ; sc, scalari- 

 form tracheides of the more external 

 primary wood. On the left is the 

 pith. X about 160. Phil. Trans. 

 W. and S. Will. Coll. 20 A. 



