54 PLANT LIFE ON THE FARM. 
in wide curves till they come in contact with a support 
round which to twine,* and thus remove their leaves 
from the surface, where they would be overshadowed, to 
a point of vantage where they would be exposed to light, 
and this with the least expenditure of material. Very 
similar are the movements executed by stolons and run- 
ners, as of the strawberry, and probably, though the 
cases have not been studied, of the trailing rhizomes of 
the twitch (Triticum repens), the scions of the meadow 
poa (Poa pratensis), of the clovers, of the milfoil, etc. 
Such a movement would facilitate the introduction of 
these runners between other plants, and thus secure the 
extension of their area of growth. The movements in 
the stem are more especially connected with growth ; 
they cease, or become much enfeebled after growth is com- 
pleted or arrested. Under certain circumstances, however, 
the faculty of growth is retained in certain spots after it 
has ceased elsewhere, or if actual growth do not take 
place, yet some of the phenomena connected with it may 
occur. Thus the stems of grasses, such as of wheat, are 
provided with thick ‘‘nodes” or joints at the places 
whence the leaves spring from the stem. When the 
wheat gets beaten down or laid by a storm of rain and 
wind, the resumption of the erect position is effected by 
the medium of the nodes, which grow, or at least become 
turgescent, especially on the under surface, which thus 
becomes convex, while the upper surface, which does not 
grow, or at least not to the same extent, becomes con- 
cave ; the consequence is that the upper end of the stem 
becomes raised—as may be illustrated thus :—Let 
represent the joint of the laid stem ; then, by the agencies 
just mentioned, the straight horizontal position is replaced 
by the ascending one “ , and ultimately by the vertical one 
*See Darwin, The Movements and Habits of Climbing Plants, 
