On the twisting of the leaves on their bases on 
the horizontal shoots of the flat-leaved 
Spruces (PICEA § OMORICA) as contrasted 
with the same phenomenon in the flat-leaved 
Silver Firs (ABIES), the flat-leaved Hemlock 
Firs (TSUGA), and the Douglas Fir (PSEUDO- 
TSUGA). 
BY 
A. D. RICHARDSON. 
With Zincographs 1—10. 
In the flat-leaved spruces, in which the stomatic leaf-surface 
is morphologically the upper one, and which constitute 
Willkomm’s section Omorica of the genus P2cea, the twisting of 
the leaves on their bases on the horizontal (plagiotropous) shoots, 
in order to direct their stomatic surfaces downwards, differs 
from that which obtains in flat-leaved silver and hemlock firs, 
and in the Douglas fir, in all of which the stomatic leaf-surface is 
morphologically the under one, in being reversed in direction, 
and, as a result of this reversion in direction, in the order of 
succession in which the leaves twist on their bases from the 
position in the median plane of the shoot at which no twisting 
takes place to that at which the maximum is reached being 
also reversed. 
In a flat-leaved spruce, a leaf arising in the median plane 
upon the upper side of a horizontal shoot does not twist on its 
base, but bends forward and becomes nearly parallel in direction 
with the shoot, so that its .stomatic (upper) surface is directed 
downwards. A leaf arising in the median plane upon the under 
side of a horizontal shoot, on the other hand, twists on its base 
through 180 degrees in order to direct its stomatic (upper) 
[Notes, R.B.G., Edin., No. 1, 1900,] 
