Structure and Function of Endodermis in Abietinece 283 
leaf only 2-3 layers are found, this being the region where no breaks 
occur in the continuity of the endodermal cells. No passage cells 
were found in the endodermis above the basal region of the leaf. 
VI. Pseudotsuga Douglasii Carr. 
The cotyledon, as described by Daguillon, possesses a clearly de¬ 
fined endodermis with suberised radial walls and an undivided bundle. 
In the adult leaf the endodermis shows on the whole less development 
of thickening than is the case in either Pinus or Picea. Most of the 
inner tangential walls dissolve readily in sulphuric acid without under¬ 
going carbonisation, but they are lignified in those parts which abut 
on lignified pericyclic tissue (Fig. 9, a and b) as in Pinus excelsa. The 
outer tangential walls are all lignified and suberised, and have pits 
at long intervals. 
In one section examined a single endodermal cell was found to 
disappear entirely on treatment with sulphuric acid, none of its walls 
being thickened. This shows that passage cells occur in Pseudotsuga, 
though they appear to be very infrequent. 
This leaf is less xeromorphic than that of either Pinus or Picea 
in some respects, since only one row of lignified hypodermal tissue at 
most is present, much of the pericyclic tissue is unlignified, and 
practically no thickened pericyclic cells are present on the abaxial 
side of the leaf. On the other hand, there is a fair development of 
cuticle on the epidermis, and the endodermal cells are more com¬ 
pletely thickened than is the case in Picea . 
VII. Larix europcea D.C. 
Daguillon describes the cotyledon as having an endodermis of 
large cells thickened on some of the radial walls. 
The mature leaf shows very little development of cuticle and also 
little development of hypodermal schlerenchyma, the latter forming 
a single layer in the angles of the leaf and in the central region of 
the upper and lower face. The leaf is dorsiventral to a certain extent, 
palisade tissue occurring on the upper side and lacunar parenchymatous 
tissue on the lower. An undivided vascular bundle is usually present, 
but this may be split near the base of the leaf by a single layer of 
conjunctive tissue. 
The endodermis of the mature leaf has the inner tangential walls 
unthickened except in a few places where they abut on lignified 
pericyclic cells (Fig. 9, c ). The outer tangential walls are lignified and 
a slight deposit of suberin may be present over part of their surfaces. 
19—2 
