LAG ELEMENTS OF PLANT ANATOMY. 
ledonous stem the original bundles take part in the formation 
of the new growth. 
tegarding the development of the bundles in the embryo, 
present investigations show that in some cases the bundle of 
the cotyledon runs down into the axillary one of the root; or 
if the cotyledon has more than one bundle, these unite at its 
node and from there run down united into the root bundle. 
The bundles of the embryonic leaves immediately following the 
cotyledon take the course described for the mature plant, so far 
as the smaller number of bundles and internodes will permit. 
STEM OF DICOTYLEDONS AND GYMNOSPERMS. 
There are more variations in the character of the stem in 
the dicotyledons and gymnosperms than in any other class. 
These variations consist largely in the different courses taken 
by the bundles and in the manner in which they anastomose 
with each other. With these exceptions the greater number of 
these stems may be referred to a certain type considered as the 
normal one. 
The mature stem is covered with an epidermis which is sup- 
plied with stomata. This epidermis is 
generally replaced by a second one named 
periderm. The ground tissue consists 
mostly of thin-walled parenchyma, with 
occasional strings of collenchymatie cells. 
The bundle system of most dicotyle- 
dons, Conifers and Gnetaceae — Welwit- 
schia excepted — may be described as 
follows. ‘The bundles are collateral and 
pie te open. All the primary ones are leaf-traces. 
@ central cylinder or pith. They enter the stem bent at the nodes 
b hollow cylinder enclosing 
bundles. chollow cylinder and run downward radially in a straight 
composed of primary rind. 
course about midway between the centre 
and circumference of the stem. The stem therefore consists 
