( 1028 ) 
The curve below gives the course of a curvature of this kind. 
Deviation of the apex in mm. 
2 
m, Vn 
40min 60 120 160 200 240 280 320 360 = 400 min. 
Fig. 4. 
Course of the phototropic curvature whilst the unilateral action 
of gravity is eliminated. Stimulated with 360 M. C, S. 
It is clear from this curve that already after 10 minutes, sooner 
therefore than when gravity is opposing, a curvature becomes visible ; 
this is of course a strong argument in favour of an earlier beginning 
of the eurvature-process. After about 6 hours there comes a moment 
in which the distance from the vertical no longer increases. In order 
to facilitate a survey of the curvature | here reproduce figures made 
from drawings on frosted glass by outlining the image projected by 
the photographic lens. 
If one compares with this a curvature in which gravity opposes, 
the great difference is at once striking. In this case too, first the 
becoming asymmetric of the apex, after which the curvature affects 
more and more basal zones. After about 6 hours the greatest deviation 
of the apex is reached. If the strength of the curvature is determined 
at this moment by placing ares of different radius along the curved 
part, it is found that the coleoptile is not bent in the are ofa circle 
but consists of a series of parts with different degrees of curvature. 
Thus the zone situated fairly close to the apex is most strongly 
curved, perhaps because it is the zone of most active growth. After 
these 6 hours the curvaiure of the uppermost part decreases, so that 
a slight diminution of the deviation of the apex is observable; it is 
the beginning of the straightening out. In the more basal parts the 
curvature still increases continuously. Finally the whole upper part 
