io BOTANY 



We need not at present consider very fully the case 

 of the water-plant, and will therefore examine the 

 relations between the root and shoot in general and 

 the surroundings in which each finds itself. 



The anchorage of the plant is secured by the penetra- 

 tion of the soil by the roots. The advantage thus 

 secured is not obtained without difficulty and even 

 danger. To become fixed in the soil the plant must 

 penetrate it, a process which it can only carry out by 

 its gradual growth. The composition of the soil offers 

 certain difficulties to this penetration: it may be too 

 dense or too powdery, too dry or too wet ; it may be 

 slimy like clay, or very hard and strong. The amount 

 of water in the soil and the degree in which it contains 

 air are also factors which must be taken into account 

 in considering this growth. After a plant has once 

 established itself and secured firm anchorage, it still has 

 to deal with varying conditions of a similar nature, for 

 the character of the soil is very liable to changes, depend- 

 ing on conditions of temperature, weather, and so on. 



Besides the advantage of a firm anchorage, the root 

 depends upon the soil for the supply of certain materials 

 which ultimately aid in some way in its nutritive pro- 

 cesses. Certain minerals are necessary to every green 

 plant, many others are advantageous, some are dele- 

 terious. We are here face to face with dangers and 

 advantages which need adjustment to the plant as it 

 is growing in the soil. Such a struggle can be easily 

 observed. While all plants need compounds of nitrogen, 

 some will only flourish on soil which contains as well a 

 certain, often a large, proportion of chalk, others fail 

 entirely if the chalk is plentiful. It is much the same 

 with other constituents of the soil. 



If a plant is growing in uncongenial surroundings it 

 has but little power of adjustment to them. It conse- 

 quently dies out more or less rapidly. If on the other 



