i6 



THE BOOK OF NATURE STUDY 



seeds in glass cylindrical vessels. Cocoanut fibre is wrapped 

 in some porous paper and placed in the cylinder. The paper 

 is kept moist. The seeds are sown on the paper next the glass. 

 If exposed to the light, the radicles may be seen bending in- 

 wards and growing into the cocoanut fibre ; if the glass cylinder 

 is covered, then the roots grow straight down between the paper 

 and the glass. 



GROWTH OF THE RADICLE IN SOIL. When planting seeds in 

 soil, it is usual to make a drill i or 2 inches deep, then to sow 

 the seeds and to rake the earth gently over them. The weight 



of the soil on the seed helps to press it 

 down and keep it fixed, whilst the radicle 

 is making its way out and pushing down 

 through the soil. When the seed is not 

 pressed down in this way the root-hairs 

 which are developed behind the tip of the 

 radicle become attached to whatever sur- 

 face they may be growing on, and thus 

 hold down the upper part of the radicle, 

 whilst the tip is forcing its way downwards 

 through the soil, or sponge, or blotting 

 paper, or whatever the substance on which 

 the seed is growing. This is very well 

 seen in barley grown on blotting paper 

 kept moist in a glass jam jar. In about 

 three weeks' time the roots will be several 

 inches long, and if it is attempted to pull the 



FIG. SA. Barley grown on ,,. ,, -11 ,, , , 



blotting paper, showing seedling away, the blotting paper to which 

 root-hairs. the root-hairs have attached themselves 



will also be torn away. 



It is easy to see how a root penetrates the soil. The apex 

 is always pointed and protected by a root-cap. The tip of the 

 root grows rapidly in length and thickens. It is thus able to 

 push away the earth on all sides. Darwin compares the force 

 exerted by a growing root with that of a wedge of wood, which 

 whilst slowly driven into a crevice, is made to expand owing to the 

 absorption of water, and he remarks that a wedge thus acting 



