2 1 6 Barratt. — A Contribution to our Knowledge of the 
tuber these protoxylem elements remained relatively in their original place, 
while the remaining elements of the bundle occupied a more peripheral 
position. As the separation became more extreme, one endodermis no 
longer surrounded both parts, but separate ones encircled each portion of 
xylem (Text-figs. io(b) and 12). 
Text-fig. 11. Transverse section of a vascular bundle of an anomalous tuber of E» arvense 
close below a node. The carinal canal is clearly visible and is enclosed with the remainder of the 
bundle by a common endodermis. 
Text-fig. 12. Transverse section of a bundle from the middle of the same internode of 
anomalous tuber. The protoxylem is separated by a considerable radial distance from the meta- 
xylem, and is enclosed in a separate endodermal sheath. Much of the parenchyma separating the 
two bundles in the radial direction has been omitted, px — protoxylem; l = lacuna. x 180. 
The relatively small number and small size of the protoxylem elements 
and their separate position in this anomalous tuber thus suggest that the 
bulk of the tracheides present in the normal bundles represent the counter- 
part of the metaxylem of the aerial shoots and cone axis. 
