GROWTH. 53 



studied, of the trailing rhizomes of the twitch (Triticum 

 repens), the scions of the meadow poa (Poa pratensis), of 

 the clovers, of -the milfoil, &c. 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 en- 

 feebled after growth is completed 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 concave ; 

 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 7, and ultimately by the vertical one . 



Darwin has shown that the joints of grass stems continue 

 to exhibit movements on a small scale for a long period. 

 Supposing the stem to be "laid," such movements would 

 clearly aid the upward tendency above described, and 

 facilitate the uprising of the stem. (Darwin, Power of 

 Movement, p. 503.) 



