104 



BOTANY. 



Exercise 37. 



179. Growth of the stem. — We may use a bean seedling growing in the 

 soil. At the junction of the leaves with the stem there are enlargements. 

 These are the nodes, and the spaces on the stem between successive nodes 

 are the internodes. We should mark off several of these internodes, espe- 

 cially the younger ones, into sections about $mm long. Now observe these 

 at several times for two or three days, or more. The region of elongation 

 is greater than in the case of the roots, and extends back further from the 

 end of the stem. In some young garden bean plants the region of elonga- 

 tion extended over an area of \omm in one internode. 



180. Force exerted by growth. — One of the marvellous 

 things connected with the growth of plants is the force which 

 is exerted by various members of the plant under certain condi- 

 tions. Observations on seedlings as they are pushing their way 

 through the soil to the air often show us that considerable force 

 is required to lift the hard soil and turn it to one side. A very 



striking illustration may be had 



in the case of mushrooms which 



sometimes make their waythrough 



the hard and packed soil of walks 



or roads. That succulent and 



tender plants should be capable 



of lifting such comparatively 



heavy weights seems incredible 



until we have witnessed it. Very 



striking illustrations of the force 



of roots are seen in the case of 



trees which grow in 



rocky situations, where 



rocks of considerable 



weight are lifted, or 



Lever auxanometer (Oels) for measuring elongation of email n'-ffc in lai-o-^ vc^rArc 

 the stem during growth. Mlld,n Hits 111 large TOCKS 



are widened by the 

 lateral pressure exerted by the growth of a root, which entered 

 when it was small and wedged its way in. 



Fig. 82. 



