THE SENSES OF PLANTS. 287 



in every direction, branching here and there in 

 search of proper food. As long as the soil is 

 uncongenial they press forward, and only when a 

 good feast is discovered do they throw out that 

 broom-like mass of fibres so conspicuous on the 

 banks of rivers and creeks. A barren subsoil is 

 carefully avoided by keeping to the surface, while 

 in the rich river bottom the sour water- logged 

 alluvion is equally distasteful. On the sand-reef 

 the tap roots go down fifty feet or more and spread 

 most evenly to glean every particle of food con- 

 tained in the water which has percolated to these 

 depths. On the mountain, again, every chink and 

 cranny between the rocks is explored, the roots 

 sometimes penetrating through narrow crevices 

 into hollows where water has accumulated and 

 spreading their network of fibres over the roof, 

 down the walls, and into the pools. In some 

 cases it appears as if the roots smell the water at 

 a distance, and move straight onwards until they 

 reach it, Some epiphytes that push their aerial 

 roots down the trunks of trees in the forest, hang 

 them quite free when above the water, only allow- 

 ing them to branch out when they reach the surface. 

 In the first case, moisture is obtained from the 

 rain and dew as they trickle down the little chan- 

 nels in the bark, while in the other a reservoir 



