H9 LANGDON—DIOON SPINULOSUM [1920 



the main cylinder for each leaf, each one of these strands describing 

 a separate arc to the point where it enters a leaf base. Further- 

 more, all girdles are reported as being horizontal throughout their 

 whole extent. It is obvious, therefore, that the phenomenon of 

 girdling, as I have been able to trace it very distinctly and definitely 

 in cleared specimens of two-, three-, and ten-year-old seedlings of 

 D. spinulosum, differs in many respects from these earlier accounts. 

 Thus for each leaf or scale leaf 7-9 strands, the number varying 

 with the size of the sheathing leaf base, separate from the vascular 

 cylinder. Two of these (fig. 8 e, e l ) leave the cylinder on the same 

 side as the leaf for which they are destined and take an upward, 

 oblique course for some distance, finally passing out more or less 

 directly through the cortex into the ventral part of the petiole. 



Two other traces (fig. ga, a 1 ) leave the main stele at closely 

 approximated points on the side opposite the leaf for which they 

 are destined and pursue an upward, rather oblique course for 

 some distance. Then, curving one in either direction, they take a 

 horizontal course, describing wide arcs through the cortex and 

 sheathing leaf base, finally entering the dorsal or adaxial part of the 

 petiole, where they undergo a complicated system of branching. 

 The rest of the traces destined for this leaf (.fig. gb, b l , c, c l , etc.) 

 leave the main stele at intermediate points and assume, like traces 

 (a, a 1 ), an upward, vertical direction, finally anastomosing with 

 the two horizontal strands as they encircle the cortex. It is 

 also noteworthy that each of these lateral oblique traces leaves 

 the stem cylinder at a point slightly higher than the one preceding, 

 so that the entire course of the two girdles is gradually and spirally 

 ascending to the point where they enter the central part of the 

 leaf base. Frequently a single bundle (fig. 8 a), separating from 

 the vascular cylinder on the side opposite the leaf for which it is 

 destined, may divide soon after leaving the central cylinder, the 

 two horizontal branches swinging to right and left in wide curves 

 through the cortex and the sheathing base of the leaf, and gradually 

 anastomosing with the rest of the traces destined for that leaf. 

 The .character of the branching of these two main strands after 

 entering the adaxial part of the petiole is so clearly illustrated in 

 fig. 10 that any further discussion of this point is unnecessary. 



