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THE STRUCTURE AND FUNCTION OF THE 
ENDODERMIS IN THE LEAVES OF THE 
ABIETINEAE 1 
By ISABEL SOAR, Ph.D. 
(With 12 figures in the text) 
Introduction 
his work on the endodermis in the Abietineae was undertaken 
with a view to ascertaining, as far as possible, the structure and 
distribution of the endodermal cells. The leaves are all markedly 
xeromorphic in character, and an endodermal layer is always present. 
This state of affairs is in marked contrast to that which obtains in 
the leaves of most angiosperms where, as a rule, no definite endodermis 
can be distinguished. 
The facts observed suggest that the peculiar structure of the 
endodermis in the leaves of these gymnosperms is one of the factors 
which serve to retard transpiration. If this be so, it must be taken 
into account when considering the xeromorphy of the leaf as a whole, 
equally with such factors as the number and position of the stomata, 
the amount of sclerotic hypodermal and epidermal tissue, the re¬ 
duction of exposed leaf surface and the absence of external dorsi- 
ventrality. 
Methods 
The following reagents were found to be most useful for deter¬ 
mining the constituents of the cell wall in the endodermis. By their 
use distinction was made between suberin, lignocellulose and cellulose. 
Both microtome and hand sections were used. 
I. Iodine and sulphuric acid. 
The cellulose walls swell, become bright blue in colour and are 
finally dissolved. Lignocellulose layers are stained deep brown, and 
suberised walls yellow-brown. 
1 Thesis approved for the degree of Doctor of Philosophy in the University 
of London. 
