70 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



the angles somewhat rounded. The original vessels forming the 

 bundle, and which form the apex of the triangle, generally rest 

 on the bundle-sheath. The subsequent additions are usually of 

 larger tracheides, though sometimes, from some cause, smaller 

 vessels may be added external to the larger ones. We see the 

 same phenomenon in the vascular wedges of the axis, where 

 occasionally some very small vessels are interpolated among the 

 larger and normal-sized vessels of the xylem, and there is like- 

 wise found similar small vessels interpolated among larger ones 

 in the rootlet bundles. The phloem elements, which are very 

 delicate, are seldom preserved, but Prof. Williamson has figured 

 one rootlet bundle shewing this tissue. 1 



The rootlet bundles must have passed outwards through the 

 vascular axis in an approximately horizontal direction, as their 

 course follows the primary medullary rays. After leaving the 

 axis they bent upwards towards the growing point, and so 

 through the cortex. No specimen showing structure has yet 

 been discovered which permits of the course of the rootlet bundles 

 being traced from the point where they leave the xylem till they 

 enter the rootlet, but they were probably surrounded by a 

 bundle cylinder, for it is otherwise difficult to account for the 

 vermicular tube-like structures which Williamson has figured and 

 described in his Memoir on Stigmaria Jicoides, pp. 26-27, PL XII., 

 fig. 39. The Caulopteris gracilis. L. and H., - is founded on the axis 

 of a Stigmaria, and shows on its outer surface the collapsed 

 rootlet bundles in a similar manner to those exhibited on the 

 specimen figured by Williamson. This condition is brought about 

 by the decay of the supporting tissue, which causes the rootlet 

 bundles to fall against the vascular cylinder, and these in the 

 fossil condition adhere to its outer surface. In the two figures 

 cited the tube-like structures are too large to represent the 

 vascular trace alone. I possess a similar example, and possibly a 

 piece of the same specimen as that figured by Prof. Williamson, 

 which I received from Mr. B. Holgate. It was collected at 

 Mr. Bayles' Brickyard, Nippet Lane, Leeds. The vermicular 

 tube-like structures on my specimen are scarcely half the diameter 



1 Monog. Stigmaria, p. 32, PI. XL, fig. 62, 

 - Fossil Flora, Vol. 1L, PI. CXLI. 



