382 Boodle . — On some points in the 
rootlets in Botrychium Limaria are monarch, the bases of 
the roots bearing them are diarch ; and the base of the root 
is more likely to show primitive structure than that of the 
rootlet. For the roots of Ophioglossum vulgatum , the 
presence of two protophloems favours the hypothesis of 
reduction from diarch structure by suppression of one of 
the xylem-groups. 
Van Tieghem and Bower have both studied the passage 
of the root-stele through the cortex of the stem. The former 
described the stele as twisting through 90° on its way out 1 , 
while the latter was unable to observe this rotation 2 . 
Series of sections were made transverse to the root-stele 
on its way through the cortex of the stem, and these showed 
a distinct change in orientation. Starting from the outside, 
on entering the cortex the xylem is directed downwards and 
the phloem upwards ; but in passing inwards a twisting takes 
place which amounts, at any rate in some cases, to nearly 
90°, so that the xylem and phloem become lateral to an 
approximately vertical plane before fusing with the stem- 
bundle. This is illustrated in Fig. 8, where the sieve-tube 
on the right is about parallel with the axis of the stem, and 
thus shows the orientation of the xylem of the root. Perhaps 
the root-stele may sometimes pass in without any twisting, 
as described by Bower, but the twisting appeared to be the 
rule in the plants examined. 
Holle 3 , from sections and from an examination of the 
vascular skeleton, comes to the conclusion that each leaf-trace 
bundle, after passing down the stem for a certain distance and 
fusing with commissural bundles, bends out again as a root- 
bundle, there being one root to each leaf. 
This would give a simple explanation of the monarch 
structure of the root. Its vascular bundle would then be 
a continuation of the leaf-trace bundle, which, after passing 
down the stem, bends outwards without any twisting, and 
with no change in structure, the monarch bundle being 
1 Van Tieghem, Traite, p. 1394. 2 Bower, 1 . c., p. 73. 
3 Holle, Bot. Zeit., 1875, P* 2 5 I * 
