ADVANTAGES OF KNOWLEDGE OF VEGETABLE PHYSIOLOGY. 187 



imitate them, it is obvious, as a general rule, the more healthily 

 will they grow. Thanks, however, to this very power of self- 

 adaptation, they can accommodate themselves within limits to 

 their new environments in a hothouse, greenhouse, or open 

 border in England. Still, the more that is known about their 

 habits in nature, so much the better for the cultivator. Thus, 

 it is said that when Aucuba japonica was first introduced from 

 Japan, it was grown under glass ; but a stray plant having been 

 thrown away was discovered to have lived through a severe 

 winter, so that it has ever since been grown in the open. A 

 gardener thus finds by experience, often after many mistakes — 

 which cost money — how to grow foreign plants ; but his 

 knowledge may have been acquired laboriously ; and he may 

 even then not know why it is best to do this or that for his 

 plants. It is here that a knowledge of physiology can some- 

 times step in and tell him ; for it is the province of science to 

 investigate into causes. Nature, however, and especially the 

 department of " life," is so obscure that no scientist has ever 

 probed all her secrets to the bottom, and probably never will be 

 able to do so ; until she tells us how it is that life-forces can issue 

 out of food. However, no one can cultivate a plant at all without 

 knowing something of its physiological requirements to enable 

 it to live and thrive ; and just so far as the practical man 

 succeeds, so far is he acquainted with the main facts of physiology. 

 The question is, therefore, Does he know enough ? 



Illustbations. — It will not be amiss to review the organs of 

 a plant in order to consider briefly their functions in a general sort 

 of way. It will then be seen that there is really no great mystery 

 in physiology after all. In order to illustrate the preceding- 

 remarks let us commence with a few physiological observations 

 on germination. 



Germination. — Seeds must be moist throughout. There must 

 be a proper temperature ; and a free circulation of air. The first 

 and second are necessary in order that the various chemical 

 changes may take place within the seed ; the third is required 

 for respiration. This shows the importance of avoiding too great 

 a depth or too wet a soil. The radicle, on protruding, points 

 earthwards. This is due to gravity. If the radicle be placed 

 in a horizontal position, gravity acts on the tip ; but the 

 influence is conducted to a certain distance behind it, where the 



