IO 



siderable and causes the "bleeding" of plants, as the 

 active exudation of sap is called. This occurs sometimes 

 when trees and shrubs are pruned too late in the spring; 

 after the sap has begun to rise. The active absorption of 

 water takes place in the young roots a little way behind 

 the root-tip, where the root can be seen to be covered bv 

 a mass of delicate hairs which, possessing very thin walls,, 

 offer great facility for the penetration of the water. It is 

 important, therefore, in transplanting young plants from 

 a seed bed or pan to injure as little as possible the delicate 

 young roots, as by pulling instead of carefully digging 

 up young plants the absorbtive part of the root anchored 

 by its many hairs may be left behind in the seed bed. ' 

 Plants injured in this way will inevitably suffer a set- 

 back, as they will not be able to absorb nutriment 

 efficiently until they have developed new roots to take 

 the place of those which have been injured. 



Let us now consider the nature of the soil in which 

 the roots are growing. We have already seen that to be 

 suitable for the growth of ordinary plants it must be well 

 drained, whether we are dealing with a plot of ground 

 or with pot plants. If the earth becomes water-logged 

 the roots are deprived of the necessary air and soon die 

 away. The -physical condition of the soil is therefore as 

 important as its chemical composition. In nature, soils 

 are not all equally porous. Some therefore require the 

 careful attention of the cultivator. Clay soils particularly 

 are liable to retain too much water and need to be 

 specially treated for successful cultivation. The retentive 

 power of a soil depends largely on the size of the particles 

 of which it is built up. Gravel or coarse sand allows the 

 water to pass through it more rapidly than fine sand, and 

 even the finest sand is composed of larger particles than 

 those of clay. We can easily prove this by stirring up 

 sand and clay in water. The particles of sand soon settle 

 down and allow the water to clear while the water in 

 which clay has been stirred up remains muddy for a long 

 time. If, however, we add a little lime to this cloudy 

 liquid we find that it clears rapidly. This is due to the 

 " coagulation " of the very fine particles of clay which 

 become collected into larger groups, and these being 

 heavier than the single particles of clay, fall to the bottom 

 of the water and allow it therefore to become clear. It is 

 upon this action of lime upon clay that the practice of 



