1898-99.] MORPHOLOGY OF THE CENTRAL CYLINDER IN THE ANGIOSPERMS. 609 
until it becomes nipped into two. I have not seen anything that would 
lead to a similar conclusion. The transitional phenomena in the seed- 
ling and also the extreme variability in certain species of the most import- 
ant characteristics of Polystely, give strong support to the opinion that 
Polystely is not a primitive feature of the group of Primulas, in which it 
is found, but a comparatively recent modification.” On a later page 
(322) he writes: “One result appears clear: that in the Primulas the 
gamostelic condition is more primitive and nearer normal monostely 
than is the dialystelic (polystelic) type, and that probably a gamodesmic 
condition preceded either.” 
The writer’s observations have been made entirely on P. Auricu/a and 
P. farinosa. The so-called monostelic species, P. s¢nenszs, P. obcontca, 
and P. Forbesi?, have been studied for comparison. The writer’s results 
in the case of P. Auricula correspond very closely to those reached in 
the same species by Gwynne-Vaughan™. As was long ago noticed by 
Kamienski™ the epicotyledonary central cylinder remains an unmodified 
single strand until several leaf-traces have been given off from it. About 
the region of exit of the fourth or fifth leaf, it becomes a stelar tube with 
the usual foliar gaps. As soon as the central cylinder becomes tubular, 
the traces running to each leaf become three in number, the largest of 
which comes off from the bottom of the foliar gap, while the two smaller 
lateral traces are derived from the vascular tissues forming the sides of 
the gap. It is only by following a series of sections that the really 
cylindrical character of the stelar system can be made out, since the 
foliar lacunz overlap and there is thus presented the appearance of com- 
pletely isolated strands. It is only necessary in this connection to 
emphasize the statements of Gwynne-Vaughan quoted above, that Van 
Tieghem has overlooked the influence of the leaf-traces on the conforma- 
tion of the central cylinder, and that there is no evidence of the repeated 
bifurcation of the primitive stelar strand, such as he describes for this 
and other so-called polystelic species. 
The writer's study of the young stem of P. farznosa has resulted in 
very similar conclusions. In this case the problem is simplified by the 
fact that the individual leaves receive but a single strand from the cauline 
stelar system. In the quite young axis, the stele does not immediately 
become tubular. Above the point of origin of a leaf-trace, the pericycle 
sinks into the stele, forming a sort of medulla (photograph 7, plate 8), 
which may be compared with that composed of both phloém and peri- 
23. Op. Cit., p. 320. 
24. Vergleich Anat, d. Prim., 1878., p, 28. 
