184 LIBERATION OF CARBONIC ACID IN GERMINATION. 



than the hard ones), and which is only prevented from becoming 

 manifest, by the mode in which the decomposed particles are 

 thus separated and carried out of the system, their places being 

 supplied by others newly deposited from the nutritious fluid. 



282. Now this process of Respiration is as constant and uni- 

 versal in the Vegetable Kingdom as it is in the Animal; and it 

 is only because a change, apparently of a contrary nature, some- 

 times obscures its effects, that it is not generally recognised. In 

 fact, a healthy plant placed in a limited quantity of air, and ex- 

 posed to the usual amount of daylight, will (so long, at least, as 

 it remains healthy) add to its purity ; and will even restore the 

 freshness of that, which, has been vitiated by an animal. But it 

 is not the less true, that there is a constant extrication of car- 

 bonic acid ; for this may be very easily proved to take place, 

 even while carbon is being absorbed. If, for instance, a few 

 small healthy plants be placed under a glass vessel, from which 

 all carbonic acid has been previously removed, and allowed to 

 remain there even in sunlight for a few hours, they will be 

 found to have set free a small portion of carbonic acid ; this may 

 be detected, by shaking the air contained in the vessel with some 

 lime-water, which it will render turbid. When the same expe- 

 riment is tried in the shade, or by night, the quantity of carbonic 

 acid found in the air is considerably greater. 



283. There are two periods during the life of a Plant, when 

 this liberation of carbonic acid gas goes on with great energy. 

 One is in the Germination of the seed ; and here we can dis- 

 tinctly trace the object which is gained, by the abstraction of the 

 oxygen from the surrounding air, and by the conversion of it 

 into this gas so opposite in its properties. In the seed, when ap- 

 proaching maturity, a considerable quantity of starchy matter is 

 laid up for the nourishment of the embryo ; and this may remain 

 unaltered for a long series of years, if the seed be not placed in 

 those conditions which excite it to grow. But if it be exposed 

 to warmth, moisture, and air (or any mixture of gases contain- 

 ing oxygen), it will sprout or germinate. In this process the 

 starch, which (while it remains such) is unfit for the nourish- 

 ment of the embryo that is being developed, is converted into 



