200 



PLANT LIFE. 



when grasses are blown down or trampled their stems erect 

 themselves by the geotropism of this basal growing zone 

 (fig. 196). 



Fig. 196. — Part of a wheat-stalk, showing strong geotropic curvature. The shoot was 

 placed horizontal, and the growth of the basal part of the internode with the leaf-sheath 

 connected with it was stimulated on the under side, the upper remaining short. No 

 curvature occurs in the older part of the internode. About two thirds natural size. 

 —After Pfeffer. 



Fig. 197.— Root-cage. On the lower edge of a sheet of zinc a little larger than the panes 

 of glass selected is formed a water-tight trough of the same material. Two panes of 

 glass of suitable size are clamped together, with a piece of wood 1 cm. thick on three 

 edges to keep them separate. Seeds are sown in fine soil evenly packed between the 

 panes ; these are set with the lower edge in the water-trough and a sheet of zinc is 

 used to keep out light. The cage should be slightly inclined, as shown, so as to keep 

 roots against the glass. — From a drawing by J. C. Arthur. 



