Vines , — On Epinasty and Hyponasty . 427 
in the dark chamber exposed to weak diffuse light entering 
through a side-window, a mirror being placed behind the plant 
so as to equalise the illumination on the two sides. Another 
plant was rotated on the clinostat under the same conditions 
of illumination. The position of the plant on the clinostat 
was such that the flat surface of the thallus was at right angles 
to the long axis of the machine, and that the direction of the 
incident rays of light was perpendicular to the long axis of the 
machine, and parallel to the flat surface of the thallus. The 
same window and mirror illuminated both plants. Exposure 
to light was considered necessary in view of the probably long 
duration of the experiment ; but it is evident that, under the 
conditions of the experiment, no heliotropic effect could be 
induced. 
The experiment commenced on July 29, and continued until 
August 9. In three days the ends of many of the branches of 
the thallus commenced to curve away from the surface of the 
soil in both the plant in the normal position and that on the 
clinostat, and this position was retained and became more 
marked throughout the duration of the experiment. 
It is on this observation and those which precede it that I 
base the conclusion that the curvatures of dorsiventral mem- 
bers which have hitherto been ascribed to negative geotropism 
are not due to this cause, but are the expression of an in- 
herent more active growth of the lower side, that is, of 
hyponasty. 
The results which I have obtained establish conclusively 
that epinasty and hyponasty are important factors in deter- 
mining the position assumed by growing dorsiventral members ; 
and that therefore no observations on the action of gravity or 
of light on such members are conclusive unless the hyponastic 
or epinastic state of the member has been previously ascertained 
and duly taken into account. 
With this I conclude the account of my principal observa- 
tions, and it only remains to briefly discuss the various forces 
which determine, in the plants which I have observed, the 
position assumed by the dorsiventral members under normal 
