666 Proceedings of Royal Society of Edinburgh. [sess. 
the sieve tubes of the phloem is a mass of cells, elongated and 
pointed as seen in longitudinal section, and with but a thin layer 
of protoplasm lining the wall of each. These are the young peri- 
cyclic fibres. The mass of fibres at a later stage is often not 
continuous, hut is broken up to two or three divisions by the 
interposition of parenchyma cells. 
Higher up in the hypocotyl the parenchymatous layer men- 
tioned above dies out, and the pericycle fibres come to lie directly 
within the endodermis. 
Pericycle fibres are also found to the outside of the foliar 
bundles a , b , c, etc., the number present and the amount of thick- 
ening depending on the age of the hypocotyl and the level at 
which the section is taken ; hut these are always less than in the 
case of the cotyledon traces. The number of pericycle fibres 
increases till the oldest part of the bundle is reached, i.e., at the 
level at which it goes off to its respective leaf. 
To the inside of each bundle, in transverse section, a conical 
cap of small celled tissue is to be seen. This surrounds the pro- 
toxylem, and extends up the flanks of the bundle till it meets the 
pericycle cells on either side (fig. 27). In radial section these 
cells form four or five layers of elongated cells to the inside of the 
innermost protoxylem elements (fig. 29). Higher up, masses of 
small cells are also found investing the foliar traces, hut the cap 
is composed of fewer cells, and has not the same conical form as 
in the case of the cotyledon traces. Where the cotyledon and 
foliar bundles are nearly of the same size, as sometimes happens at 
the level represented in fig. 12, it is always possible to distinguish 
between them by means of this comparison. 
When the cotyledon traces go off to the petioles, they take with 
them their investments of small cells, consisting of the inner caps 
and their segments of pericycle (i.e., peridesm of Yan Tieghem) 
and corresponding arc of endodermis. 
Epicotyl. 
In the young epicotyl the character of the transverse section 
has somewhat changed. The eight traces have left for the cotyle- 
dons, and there is now a ring of foliar bundles of varying ages, 
