ENDOSMOSE. 693 



a piece of bladder over the expanded end and fill it partly with syrup or 

 gum-water, so that this shall rise in the stalk about an inch ; place this in a 

 glass of water with the bladder downwards, and the fluid will be seen slowly 

 to rise in the stalk, so that in perhaps an hour it will rise to the top. This 

 apparatus resembles one of the spongioles at the extremity of the fibre of 

 a root. 



The rain falling through the air carries with it a certain amount of 

 carbonic acid and ammonia, which the air always contains, and it is the 

 whole source of the nitrogen which forms a very important part of the 

 bodies of plants and animals. When the rain arrives at the surface of the 

 earth, it sinks down into it and carries with it all soluble vegetable or 

 animal matter which it meets with, together with any soluble earthy matter 

 which may exist in the soil ; this forms the sap of the tree. When it 

 arrives at the surface of the leaf, the watery part of 

 it combines with the carbonic acid of the air (through 

 the influence of light), and appropriating its carbon, 

 gives out the oxygen ; this is the true respiration of 

 plants, and is exactly the reverse of what takes place 

 during the respiration of animals, in which case oxygen 

 is absorbed and carbonic acid given off. The carbon 

 thus retained by the plant combines with the elements 

 of the water to form the solid green substance called 

 chlorophyl, which is the basis of all the tissues of the 

 plant ; the ammonia is also decomposed, and its nitro- 

 gen combining with the oxygen and hydrogen of the 

 water, and the carbon of the carbonic acid forms those 

 compounds which constitute the most nourishing parts 

 of vegetables, such as albumen, gluten, etc., and of 

 which all the animal tissues are built up, for the pro- 

 duction of these organic substances takes place in the 

 vegetable only, animals simply appropriating them 



for their food. The sap which reaches the leaf is not all converted into 

 chlorophyl, but also into those peculiar juices which are found in plants, 

 some of which contain sugar, some gum, others (as the pine tribe) turpen- 

 tine, and in the laurel tribe camphor, all of which are substances containing 

 much carbon ; moreover the solid wood and bark are deposited from these 

 juices as they descend from the leaf after having been acted on by light (or 

 the actinic power associated with it). Now, as the water, ammonia, and 

 carbonic acid which descend with the rain are from the air, and as the 

 vegetable is formed wholly by their absorption, it may be fairly said that 

 the vegetable kingdom (and therefore the animal) feeds upon the air, and 

 that the trees do not grow out of the earth, but into it. 



