504 Tansley and Chick. — On the Structure 
base the epidermis and cortex of the leaf resemble those of 
the stem, but at 1 cm. up, the characteristic mesophyll and 
leaf-epidermis make their appearance. The mesophyll is 
distinctly peculiar (Figs. 6 and 8). It consists of very long 
cells running parallel to the axis of the leaf, with rows of 
lateral lobes coming off horizontally and joining the similar 
lobes of other cells so as to leave rounded or angular lacunae 
between the cells. The lobes sometimes have two arms and 
are irregular in size and shape, so that they enclose a very 
irregular network of lacunae (Fig. 6), though they themselves 
form fairly even longitudinal rows, each row containing eight 
or ten lobes (Fig. 8). All the mesophyll cells are alike in 
structure and contents. 
The epidermal cells are thick-walled, broad, and of con- 
siderable length. The stomata are arranged in two longi- 
tudinal rows on the morphologically lower surface of the leaf. 
In each row every alternate cell becomes the mother-cell of a 
stoma. The guard-cells project slightly from the general 
surface of the leaf. Their length is three or four times as 
great as their transverse diameter. The inter-stomatic cells 
(; i . st. c. in Figs. 6 and 8) of the stomatiferous rows are shorter 
and deeper than the ordinary epidermal cells. 
The Anatomy of the Root. 
This corresponds with Prantl’s description and illustration 
of S'. Pennula 1 , but we have thought it well to figure a 
transverse section of the stele (Fig. 9), as the cells of the 
phloem are not shown by Prantl. 
Development of Tissue-systems at the Apex of 
the Stem. 
The growing-point of the stem of this plant is rather 
variable in form. The free apical surface is always flattish, 
and sometimes forms a perfectly plane surface at right angles 
to the long axis of the stem. More usually it is slightly 
convex. There is a well-defined apical cell of an approxi- 
1 Prantl, op. cit., p. 38, Taf. IV, fig. 59. 
