58 PLANT LIFE ON THE FARM. 



The Action of Moisture on Boots. Much more 

 obvious to the general observer is the action of moisture 

 on roots. The distance to which roots will travel in search 

 as it were of water, and the way in which luxuriant growth 

 and intricate ramification are promoted, when access 

 to it is obtained, are familiar facts. Too frequently drain 

 pipes get choked with a mass of roots whose structure 

 has been changed, and whose excessive growth has been 

 stimulated by the presence of copious supplies of moisture. 

 If there is an equal supply of water all round, the growth of 

 the roots will be uniform ; but if, as is more often the case, 

 there is more water on one side than on the other, then 

 the root will curve to the side where there is the fullest 

 supply, and the power thus exerted to get at the water is 

 greater than that of gravity. When the tip of the root is 

 covered with grease, the root does not bend to the wet 

 surface, on which account Mr. Darwin and his son infer 

 that sensitiveness to moisture resides specially in the tip. 

 The relation these movements and this growth bear to the 

 processes of nutrition carried on by the root is too obvious 

 to need further comment. N 



The Influence of Contact on Boots The effect of 

 pressure such as that caused by the contact of any 

 substance, even if it be very slight, is to produce move- 

 ments of curvature in the root, the direction of the 

 curvature varying according to the part of the root touched. 

 Thus, if the root be touched in the region where growth is 

 going on most actively, the root becomes concave on the 

 side which is touched, convex on the opposite side, pro- 

 bably because growth is arrested by the pressure on the 

 one side, while it is unrestricted on the other. The con- 



