664 Proceedings of Royal Society of Edinburgh. [sess. 
epicotyl of our seedling, we seem to get some light on the 
important topic of the relation of the bundle to the stele. 
Root and Transition Region. 
The pericycle in the root proper is represented by a band of 
varying thickness, consisting of layers of thin walled cells a little 
smaller than those of -the endodermis. Since the outline of the 
cylinder is circular, and the xylems are placed nearer the centre 
than the phloems, these cells form wedge-shaped masses eight to 
twelve cells deep opposite the protoxylems, but opposite the 
primary phloems the pericycle narrows down to two, or in some 
cases one layer between the outermost point of the phloem arc 
and the endodermis. The innermost vessels of the primary xylem 
abut directly on the large cells of the pith; the phloems are 
separated from it by several layers of external conjunctive 
(%• !)• 
In the phloem itself, even in quite young specimens, fibres are 
to be found. These are in many cases lying side by side with 
sieve tubes and companion cells, and there can be no doubt as to 
their origin from the phloem, and not from the pericycle. The 
line of demarcation between the two is quite clear (fig. 25). This 
occurrence of fibres in the primary phloem of the root is rare, 
according to Yan Tieghem,* who records them only in Legumino- 
sese and Malvales including Malvaceae, Sterculiacese, and Tiliacese, 
in certain of the Cycadese, and in Anona and Celtis. 
In the transition region, after the split protoxylems have turned 
towards the centre of the cylinder, and the stele consistsof four double 
stem bundles (figs. 5, 26), the interfascicular pericycle consists of 
a band of seven to eight, or even more, layers of small thin 
walled cells connecting these bundles, but not stretching down- 
wards to their protoxylems. This band is in the position of the 
wedge-shaped mass of pericycle opposite the protoxylem mentioned 
above, and it is from it that the lateral roots are seen to arise. 
In the root arrangement the protoxylems are surrounded by 
small celled tissue (the pericycle). Some of this remains in con- 
nection with the protoxylem during its rotation, so that when the 
* Yan Tieghem, Ann. Sci. Nat. Bot., ser. 7, 1888. 
