
140 THE BEHAVIOUR OF PLANTS 
on the plant grown in the dark with those on the plant 
grown in the light. The plants are of the same age. 

mee ee wm om mw ew we we ww ew 
me 
° 
; 
Fic. 170. Sunflower seedlings 
grown in light, just covered 
to exclude light. 
light they spread apart and expand. {| 
What causes them to open and expand? 
Let us cover some marrow seedlings | 
which have grown in the light, and in _|j 
_ which the cotyledons have just expanded. {& 
The box should be tight so that the seed-  Vié=< 
lings will be kept in the dark. Allow We uff ii 
them to remain here a day or two; then | 
Light, then, increases the size of 
the leaves of such plants as the © 
marrow, sunflower, buckwheat, 
etc. How is it with the wheat 
and similar plants ? 
Do the cotyledons of the vege- 
table marrow open in the dark? 
As the cotyledons of the marrow 
slip from the seed coats and are 
pulled out of the ground by the 
loop, they are clasped tightly 
together. But as 
they are straight- wy 
ening up in the 

eee; 
or Fa 
LL Lae 
a Ay ey 
> . * —e 
vt) 
abeese: 
Fiqa. 171. Same seed- 
remove the box sometime near mid-day. lings after being 
The cotyledons are clasped together and 
erect, as in Fig. 171. 
covered two days. 
Now leave them uncovered ; the 
