IN SPRUCES AND FIRS 23 
The effect of this twisting of the leaves on their bases on 
the horizontal shoots of the firs and spruces referred to results 
in but a slight deviation from. the normal condition of the 
internal leaf-structure, and this only in the flat-leaved spruces. 
In the flat-leaved silver and hemlock firs, and in the Douglas 
fir, there is no departure from the normal condition, and 
the arrangement of the internal tissues of the leaf is precisely 
the same both in leaves of the leader shoots (where no twisting 
takes place) and in leaves of the horizontal shoots ; but in the 
flat-leaved spruces, owing to the stomata being located on the 
morphologically upper leaf-surface, and to the consequent 
inversion of the leaves on the horizontal shoots as compared with 
those on the leader (erect) shoots, or with those on both the erect 
and horizontal shoots of a flat-leaved silver fir, or the Douglas fir, 
the positions of the various leaf-tissues are completely reversed, 
so that the phloem is towards the non-stomatic, actually upper 
(but really morphologically under) side, and the xylem towards 
the stomatic under (but really morphologically upper) side, 
while the resin-canals occupy their normal positions on the phloem 
side of the leaf. The only anatomical change which results 
from this abnormal (inverted) position of the leaves on the 
horizontal shoots of these flat-leaved spruces is the formation of 
palisade cells in the non-stomatic upper (but really morpho- 
logically under) side of the leaf in two or three of the species ; 
and no doubt it is the abnormal position of these cells on the 
same side of the leaf as the resin-canals (which always belong 
to the under side of the leaf!) that has led to the little 
*€ one on either side of the branch (in which case the leaves are nearly at a right 
‘angle to the branch), and one in the median plane of the upper surface (in which 
“case the leaves are appressed along the branch arpa: to its main axis). The 
“* median leaves are usually smaller than the lateral ones.’ 
It is quite true, as Dr. Masters says, that in hemlock firs like 7suga canadensis the 
leaves are really arranged in three groups, but such a description is incorrect when 
es to any of the flat-leaved silver firs, as has been shown in this paper. 
1In connection with this it may be pointed out here that the figures of the 
erse sections of 2 leaves a Picea Alcockiana and P. Glehnit of the ** Gardeners’ 
Chaonicte” (Vol. xiii, N.s., pp. 212 and jor) and of the ‘Journal of the Linnean 
Society”’ (Botany, Vol. xviii, pp. 509 and 513) are, judging from the positions of 
these r eos, evidently inverted, as is also spoareiikty that of ?. Breweriana of 
the ‘‘ Gardeners’ Chronicle” (Vol. xxv, N.S., p. 497). In the two first-mentioned 
species no twisting takes place at the bases of the leaves on the horizontal shoots, so 
* 
