200 
A. G. Tansley. 
the gap in the second cylinder made by the passing off of the dorsal 
tongue; so that the final adaxially directed limbs of the lateral 
loops (the last to appear in evolution) are actually supplied from 
part of the second cylinder in front of the base of the trace. The 
considerable demands thus made by the trace lead to the appearance 
of a third cylinder (W and X), which arises as an elaboration of the 
edge of the gap in the second at a point anterior to the dying out 
of the flanges referred to. This third cylinder, which may be either 
haplostelic, of Lindsay a-type (X) or solenostelic (W), is only found 
in the largest rhizomes with the largest leaf-traces. 1 
Fig. 62. Saccoloma adiantoidcs. Two diagrammatic transverse sections 
of the stem showing stages in the detachment of the leaf-traces, and the 
accessory internal cylinders. In 13 the beginnings of a fourth system. From 
Mettenius. 
Fig. 63. Saccoloma adiantoidcs. Stages in the formation of a leaf-trace 
from the external cylinder. In the last figure the detachment of a strand from 
the second cylinder which will fill the leaf-gap. From Mettenius. 
The above summary of the main facts of structure of this 
complex vascular system clearly shows that it is developed along 
the lines suggested by Gwynne-Vaughan, and further that each 
1 For further details and additional figures of the vascular system 
of Matonia , see Tansley and Lulham, ’05. 
