of the organic matter necessary for nutrition. We 

 have further learned that this organic matter has to 

 undergo certain transformations, summed up under 

 the word digestion, before it can be incorporated 

 into the protoplasm of either kind of organism. At 

 the same time it is worthy of note that the diges- 

 tive apparatus is less complex in the plant than 

 in the animal, because the green plant is able 

 to construct the primary organic compounds best 

 suited to its wants, whilst the animal, being unable 

 to do so, must accept those already formed by 

 other organisms, and these compounds are not 

 always those most appropriate to its immediate 

 necessities. 



A few words of explanation must be added as to 

 the modes of nutrition of non-green plants. Some of 

 them are parasites living at the expense of living 

 plants or animals ; such plants are virtually thieves, Parasites 

 since they appropriate the compounds manufactured 

 by others for their own use. Parasites also occur 

 in the animal world. Other organisms, again, be- 

 longing either to the vegetable or animal world, are 

 either saprophytes, or saprozoa, that is to say, 

 plants or animals which live on non-living organic Sapro- 

 substances, compounds which have been manu- ^5 tes 

 factured by living organisms, or which result from saprozoa. 

 the decomposition of their dead bodies. 



There are, however, other types of nutrition in the 

 plant world worthy of mention ; it will suffice to specify 

 two of these. Other plants, moreover, are symbionts, Symbionts. 

 that is to say, organisms which live with others but 

 not precisely at their expense, since, although they 

 depend upon their partners for certain products, 

 they give to their partners certain other products 

 which they themselves have manufactured. There 



