132 
Sydney H. Vines. 
which the glass jar containing the plant in au atmosphere free from Cü 2 , 
was exposed for a time to light. The following is one of tbese experiments. 
Time. 
Honrly 
growth. 
Temperature. 
7—S 
a. m. 
1.10 
22.4 0 C. 
9 
1.20 
22.4 
10 
1.30 
23.5 
t H' 
1.50 
24.0 
1 y 12 
— 
1.40 
24.8 
1 
p. m. 
1.30 
26.4 
2 
1.50 
25.8 
3 
1.70 
25.0 
4 
1.70 
25.3 
5 
1.80 
24.6 
ß 
1.60 
24.2 
7 
1.50 
24.0 
These experiments prove that the retarding effect of the action of 
light upon their growth can be produced when the leaves are not assi- 
milating. They afford also some data for the discussion of another of 
Stebleu’s conclusions, namely, that a daily periodicity is perceptible in 
the growth of the leaves of etiolated Monocolyledonous pianls, which 
he believes to be an inherited property. It this be so, it is evidently 
unnecessary to ascribe the daily periodicity of the growth of green 
leaves to variations in the aclivily of the process of assimilation, for 
they, doubtless, are in possession of this inherited peculiarity as well 
as etiolated leaves. Still more unnecessary is it to assume, as Stebi.er 
does, that the property possessed by green plants of so reacting to light 
that there is a greater growth during the day, is inherited. 
1 do not propose to discuss any further at present the question whe- 
ther or not a daily periodicity of the growth of vegetable orgaus exisls 
which is quile independent of variations in external conditions, for it is 
beside the principal objecl of this paper. 1 would simply call attention 
to the fact that, in his observations upon the growth of internodes, Sachs 
failed to discovcr any such independent periodicity, that the experiments 
of Prantl upon the growth of the leaves of Dicotyledons and the obser¬ 
vations of STREnL upon the growth of roots, render its existence in thcse 
organs improbable, and that I have been unable to delect it in the 
above mentioned experiments. 
The following are the principal results arrived at: 
1) 1 hat it is possible for leaves to grow when they are not assimilating. 
That the effect of light in retarding growth is exhibited by lea¬ 
ves which are not assimilating. 
3) That, therefore, the daily periodicity observable in the growth 
ol leaves of Monocoty ledons) is not a funclion of assimilation, 
but is an expressiou of the effect directly produced upon the 
growing cells by the alternalion of day and night. 
