30 



LECTURE II. 



the roots of bulbous plants, but also on other thick root-fibres. It is clear that; 

 from the place where a root-fibre has closely applied itself to the soil by means of 

 its root-hairs, this shortening of the older tract of fibre must tend forcibly to 

 draw its point of attachment back to the mother root, or to the part of the stem 



4'l3 



whence it rises. A vertical tap-root will thus be drawn tight in various 

 directions by its numerous side rootlets, very much as the mast ' df a ship 

 is strained and made fast in different directions by the cordage. This ten- 

 sion, arising from subsequent shortening, shows itself especially in the aerial 



