404 West. — A Contribution to the Study of the Marattiaceae . 
Fig. 13) for Angiopteris and Marattia , were frequently found completely 
blocking the lumen of the protoxylem elements of the vascular strands 
both in the stem and in the petiole. 
6. Leaf Structure. 
The adult leaf of Danaea nodosa and of Danaea alata has a leathery 
texture, and exhibits histological characters which are generally associated 
with a xerophytic habit. In other words, the leaf is provided with a thick 
cuticle, whilst the ground-tissue of the lamina exhibits differentiation into 
a palisade layer and spongy mesophyll ; large intercellular spaces occur in 
the latter. Numerous stomata are found on the lower surface of the leaf ; 
as Campbell ( 20 , p. 152) has already pointed out, each fully developed 
stoma is surrounded by a series of accessory cells, which are more or less 
spirally arranged. 
7. Root Structure . 
The general anatomical structure of the root, which is identical 
throughout the family, is already well known and needs no further 
Text-fig. 33. Diagrammatic transverse sections of roots of (a) Danaea aiata , Sm., 
(b) Danaea nodosa, Sm., and (c) Kaulfussia aesculifolia, Bl. nye. — mucilage canal ; si. = stereome. 
All x 10. 
description. However, a comparative study of the distribution of stereome 
in the roots of the first order in the various genera and species of 
Marattiaceae is of interest, since it can readily be correlated with the 
general habit of the plant. 
In the principal roots of Danaea nodosa and of Danaea simplicifolia , 
two of the radial species, the stereome forms a fairly wide zone near the 
periphery of the cortex, whilst lignified tissue (excluding the tissues of the 
xylem) also occurs in an axile position (Text-fig. 33, B). Considered from 
the point of view of mechanical efficiency, this distribution of the stereome 
would enable these roots to withstand effectively both crushing and pulling 
strains. Now, although the basal portion of the massive more or 
