IN SPRUCES AND FIrs. 21 
Fig. 7 represents the positions assumed by the leaves in 
flat-leaved silver firs, in some hemlock firs, and in the Douglas 
fir when such a shoot as that represented in Fig. 6 becomes 
horizontal. The leaves corresponding to those in Fig. 6 are 
indicated by corresponding numbers, and the degree-numbers 
indicate the angles through which the leaves twist on their bases, 
as well as their angular divergences from the leaf in which no 
twisting takes place. 
_In Fig. 7, leaf 7, which is in the median plane upon the under 
side of the shoot, is the one in which no twisting takes place, 
but, by the swing movement on its base already referred to, it 
moves upwards and outwards to the position indicated in the 
figure, As, however, its point of insertion is in the median 
plane of the axis, it may move either to the right or to the left. 
In leaf 1, which is in the median plane upon the upper side of 
the shoot, on the other hand, the maximum amount of twisting 
at the base takes place, and owing to its being in the median 
plane of the shoot, it may, like leaf 7, move either to the right 
or to the left. In those lying between 1 and 7, on either side 
of the median plane of the shoot, the amount of twisting which 
each undergoes is equal to the angular divergence of its point 
of insertion from that in which no twisting takes place, as 
indicated in the figure. For example, the points of insertion of 
leaves 4 and 10 are each divergent 90 degrees from that of leaf 
I, and this is equal to the angle through which each twists 
in order to bring its median plane into a vertical position. 
The curved arrows above and beneath Fig. 6 indicate the 
direction in which the leaves shed away from the median plane 
of the axis, on the upper side by twisting, and on the under side 
by a swing movement at the base, when a shoot such as this 
becomes horizontal as in Fig. 7. 
Figure 9 represents the positions assumed by the leaves in a 
flat-leaved spruce when a shoot such as that represented in Fig. 8 
becomes horizontal, and the leaf-numbers and degree-numbers 
have the same significance as those in Fig. 7. Leaf 1 in Fig. 9 
is that in which no twisting takes place, and it retains precisely 
the same position in relation to the axis as does the corresponding 
leaf in Fig. 8. In leaf 7, on the other hand, the maximum 
amount of twisting on the base takes place, and in addition 
