222 Barratt. — A Contribution to our Knowledge of the 
in the internode they occur also internally to the separate strands of xylem.’ 
It may be stated quite definitely that these elements belong to the proto- 
xylem, although Browne does not apparently identify them as such, and, as 
will be shown below, they form a definite system of strands and constitute 
the scaffolding on which the whole vascular system of the cone is built up. 
The species examined were E. maximum , E. arvense , E. limosnm , 
E . palustre , E. sylvaticum. 
In very young cones of E. palustre' 1 the development of the xylem 
could be readily made out (Text-fig. 18). It proceeds in a manner in no 
Text-fig. 18. Diagram representing half a young cone of E. palustre. The sporangiophores 
and leaves are somewhat diagrammatic, and the small circles surrounding dots in connexion with the 
vascular strands represent the points of connexion of the sporangiophore traces not otherwise shown. 
The protoxylem strands were traced with a camera lucida. 
Text-fig. 19. Xylem strand of cone and the first differentiated tracheide of the sporangiophoric 
trace from young cone of E. palustre . A = axial strand of cone ; S «= sporangiophoric trace. 
' 
way comparable with that of the vegetative axis. In the latter, the several 
protoxylem strands of each internode develop simultaneously. Their 
1 Cones of E. arvense and E. maximum were collected in the autumn and found to be fully 
formed. As Browne pointed out for E. arvense, x the vascular system is at this time practically 
mature. E. palustre was therefore selected owing to the fact that the cones are formed at the 
apices of the vegetative axes, and can be very easily collected at an early stage. 
