TEE GROUND BETWEEN ANIMALS AND PLANTS. 6^7 



The bean has been able to perform this great chemical feat by the 

 help of its green coloring matter, or chlorophj^l, which, \nider the 

 influence of sunlight, has the marvelous power of decomposing car- 

 bonic acid, setting free the oxygen, and laying hold of the carbon which 

 it contains. In fact, the bean obtains two of the absolutely indis- 

 pensable elements of its substance from two distinct sources ; the 

 watery solution, in which its roots are plunged, contains nitrogen but 

 no carbon ; the air, to which the leaves are exposed, contains carbon, 

 but its nitrogen is in the state of a free gas, in which condition the 

 bean can make no use of it ; * and the chlorophyl is the apparatus by 

 which the carbon is extracted from the atmospheric carbonic acid 

 the leaves being the chief laboratories in which this operation is ef- 

 fected. 



The great majority of conspicuous plants are, as everybody knows, 

 green ; and this arises from the abundance of their chlorophyl. The 

 few which contain no chlorophyl and are colorless are unable to ex- 

 tract the carbon which they require from atmospheric carbonic acid, and 

 lead a parasitic existence upon other plants ; but it by no means fol- 

 lows, often as the statement has been repeated, that the manufactur- 

 ing power of plants depends on their chlorophyl and its interaction 

 with the rays of the sun. On the contrary, it is easily demonstrated, 

 as Pasteur first proved, that the lowest fungi, devoid of chlorophyl, 

 or of any substitute for it, as they are, nevertheless possess the char- 

 acteristic manufacturing powers of plants in a very high degree. 

 Only it is necessary that they should be supplied with a different 

 kind of raw material ; as they cannot extract carbon from carbonic 

 acid, they must be furnished with something else that contains carbon. 

 Tartaric acid is such a substance ; and if a single spore of the com- 

 monest and most troublesome of moulds Penicilliu'm be sown in a 

 saucer full of water, in which tartrate of ammonia, with a small per- 

 centage of phosphates and sulphates is contained, and kept warm, 

 whether in the dark or exposed to light, it will in a short time give 

 rise to a thick crust of mould, which contains many million times the 

 weight of the original spore in proteine compounds and cellulose. 

 Thus we have a very wide basis of fact for the generalization that 

 plants are essentially characterized by their manufacturing capacity, 

 by their power of working up mere mineral matters into complex or- 

 ganic compounds. 



Contrariwise, there is no less wide foundation for the generaliza- 

 tion that animals, as Cuvier puts it, depend directly or indirectly upon 

 plants for the materials of their bodies ; that is, either they are her- 

 bivorous, or they eat other animals which are herbivorous. 



But for what constituents of their bodies are animals thus de- 

 pendent upon plants? Certainly not for their horny matter; nor for 



' I purposely assume that the air with which the bean is supplied iu the case stated 

 contains no ammoniacal salts. 



