VI ANIMALS AND PLANTS 175 



which the carbon is extracted from the atmo- 

 spheric carbonic acid the leaves being the chief 

 laboratories in which this operation is effected. 



The great majority of conspicuous plants are, as 

 everybody knows, green ; and this arises from the 

 abundance of their chlorophyll. The few which 

 contain no chlorophyll and are colourless, are un- 

 able to extract the carbon which they require from 

 atmospheric carbonic acid, and lead a parasitic 

 existence upon other plants ; but it by no means 

 follows, often as the statement has been repeated, 

 that the manufacturing power of plants depends 

 on their chlorophyll, 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 chlorophyll, or of any sub- 

 stitute for it, as they are, nevertheless possess the 

 characteristic 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 car- 

 bonic acid, they must be furnished with something 

 else that contains carbon. Tartaric acid is such a 

 substance ; and if a single spore of the commonest 

 and most troublesome of moulds Penwillium be 

 sown in a saucerful of water, in which tartrate of 

 ammonia, with a small percentage 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, 



