499 
Stem of Angiopteris evecta. 
states that a portion of the second zone filling up the gap 
in the first, due to the presence of a leaf, unites with the 
segment of the first zone going to the leaf, so that at the 
point of insertion of the leaf we find anastomoses between 
the two outermost zones 1 . 
Mettenius refers briefly to the structure of the stele in the 
stem and in the root, and worthy of note is the fact that 
he finds the protoxylem of the steles of the stem either 
central, or situated at the periphery of the wood nearest the 
organic axis. 
In a paper by Russow 2 in 1872, there is no investigation 
into the course of the bundles, but the much debated 
question of the structure of the root-apex first comes under 
discussion. 
Russow describes two kinds of roots: unbranched air- 
roots with twelve to twenty groups of protoxylem, the outer¬ 
most elements only being lignified, and branched earth-roots 
with five groups, the elements of which are lignified to 
the centre. 
According to Russow apical growth in the roots takes 
place by means of several cells; these are twelve to eighteen 
in number, prismatic in shape, proportionally large, and rich 
in protoplasm. The outer apical cells give rise to the cortex 
and epidermis ; the middle apical cells form the axial vascular 
strands and root-cap tissues. 
Longitudinal division occurs at intervals, and the cells 
thus formed take the place of those which have divided to 
form the cortex. The weaker earth-roots have a similar 
method of growth, but the number of apical cells present 
is smaller. 
In connexion with Russow’s paper it should be mentioned 
that the figure he gives of the apical cells in the root of 
Angiopteris evecta really represents the arrangement of the 
cells in the root-cap 3 . 
In a paper by Kny 4 , contemporaneous with that of Russow, 
1 Mettenius (’ 64 ), p. 510. 
8 Russow ( 72 ), Taf. VIII, Fig. 161. 
L 1 2 
2 Russow ( 72 ). 
4 Kny ( 72 ). 
