GROWTH 183 



continual and important loss of substance, owing to 

 respiration. 



Let us begin our survey of the phenomena of growth 

 with the moment the little root and stem emerge from 

 the germinating seed, when the one seeks, so to speak, 

 to escape from the light as quickly as possible and 

 buries itself in the ground, while the other stretches up 

 into the air to meet the light. The first question that 

 ought naturally to arise in our mind when we investigate 

 this phenomenon, but probably one which seldom occurs 

 to people, so accustomed are we to the fact, is : Why do 

 the root and stem grow in different directions, the one 

 into the soil, the other into the air ; the one downwards, 

 the other upwards ? 



This point has perplexed scientists very much, and 

 even now it cannot be considered settled in all its details. 

 In seeking the cause of this phenomenon scientists very 

 naturally turned to light and the moisture in the soil. 

 It has been pointed out that stems grow towards the 

 light and roots away from it ; and consequently it has 

 been said that light must be looked upon as the external 

 force which conditions the direction of growth. But 

 this theory is pretty easily proved to be untenable. 

 The direction of the organs in question will be the same 

 in the absence of light ; moreover, if seeds are sown 

 in a sieve suspended above a window so that they are 

 lighted only from beneath, after passing through the 

 layer of earth the roots will equally pass through the 

 holes of the sieve and continue to grow towards the 

 light, while the stems will grow upwards and therefore 

 away from the light. The other theory that the direc- 

 tion of the root is determined by the moisture of the 

 soil is disproved by an experiment, in which germinating 

 seeds are surrounded by moist earth or embedded in a 

 wet sponge. The degree of moisture in such cases is 

 uniform, and yet the direction of the root and stem will 

 be as before, perpendicular. 



