170 On the Management of Peach Trees. 



effect, as far as regards the general health or appearance of 

 the plants. Solar intluence, however, does not merely affect 

 the shoots of a growing plant, for the young roots, or sponge- 

 oles, are as suddenly, and in a similar degree, afiected. The 

 spongelets become less active, and, if it be for a short time 

 withdrawn, they lose their power of action altogether. The 

 destruction of any quantity of the foliage acts on the roots 

 nearly in the same manner as a diminution of the natural 

 quantity of light. The respiratory powers of the plant be- 

 come impaired, and the healthy action of the rootlets sus- 

 pended, if not altogether stopped. Kespiration takes place, 

 by the power, which the leaves possess, of inhaling and exha- 

 ling oxygen, and decomposing carbonic acid : oxygen is es- 

 sential to the formation of carbonic acid generated in the pro- 

 cess of respiration ; but, when this carbonic acid is decomposed, 

 and the oxygen liberated, the same oxygen which is set free 

 will serve again for a fresh formation of carbonic acid, so 

 long as there remains any carbonaceous materials in the sap ; 

 but the leaves will not accomplish the decomposition of car- 

 bon, except when in a green and healthy state ; the leaves 

 and young shoots being the principal meridian of decomposi- 

 tion, it is evident that the greater the quantity of these upon 

 the tree, the greater will be the quantity of carbon decom- 

 posed. Moreover, we learn, from scientific investigation, that, 

 during light and sunshine, plants assimilate carbon, and 

 evolve oxygen, and that, during night, and shade, this system 

 of assimilation is reversed, that is, they inhale oxygen, and 

 evolve carbon ; oxygen is assimilated to the plant ; not as it 

 is inhaled, but most probably, by means of the decomposition 

 of cabonic acid when a portion of it is retained. The most 

 obvious influence of ogygen, as applied to the leaves, is that 

 of forming carbonic acid, and thus presenting elements to the 

 plant suitable for assimilation, and consequently facilitating 

 its development. Thus, it appears that oxygen gas, which 

 has been found to be indispensable to animal life, is no less 

 indispensable to vegetable life ; and, though plants will not 

 thrive well in an atmosphere of pure oxygen, it is quite evi- 

 dent that a certain quantity is absolutely necessary for their 

 perfect development. 



But what, it may be asked, has all this to do with the cul- 



