Red Wood in Conifers. 203 
the curved region the number fell to fifteen, and in the upper part of the 
vertical region to less than eight. 
Hence this last region only received the gravitational stimulus from 
the horizontal region when three-fourths of the year’s growth of wood had 
taken place. 
A few peculiarities will be noted in the figures. Thus in the basal 
part of Fig. 3 the red wood appears on the upper inner surface of the main 
axis, on the side of the lower part, and on the inside of the upper part of 
the vertical segment. The lower part, however, formed but little wood and 
was very strongly compressed. 
Hence it is possible that very strong pressure applied to a feebly 
active cambium may overcome the gravitational influences normally re- 
sponsible for this special morphogenic response. 
In Fig. 5 red wood appears on both upper and under surfaces of a few 
lateral branches, although both the gravitational and the pressure stimuli 
act alike on the under surface. Possibly this is the result of the diffuse 
spreading of the gravitational stimulus from above and below the branch ; 
and in any case it is worthy of note that a slight deviation from the 
perpendicular is sufficient to produce a perceptible response, while the 
maximum possible morphogenic stimulus appears to be exercised by a 
comparatively small angle of deviation, beyond which but little further 
increase occurs. 
In brief, therefore, it may be stated that, as far as these observations 
go, they show that the formation of red wood is a morphogenic response 
to a gravitational stimulus which is able to spread longitudinally from 
the region where it is directly perceived, and which may under special 
circumstances be modified or suppressed by very strong pressure stimuli. 
