22 SCIENCE PRIMERS. [v. 



matters containing nitrogen, such as nitrates or salts 

 of ammonia. From these in some way or other not 

 yet understood, but under the influence of protoplasm, 

 the nitrogen is abstracted, and from this, together 

 with the constituents of starch, albuminoids are 

 manufactured. 



These albuminoids are the necessary food of proto- 

 plasm. It is important to remember that their 

 formation depends upon the manufacture of starch in 

 the green parts of plants, and this depends upon expo- 

 sure to sun-light. We see, therefore, why without light 

 plants starve; their protoplasm ceases to be nourished. 



29. The effect of plants requiring mineral sub- 

 stances for their nourishment is, that one kind of crop 

 cannot be grown continuously on the same piece of 

 ground, if it is periodically cut and carried away. 

 This has led to the use of manures containing the 

 substances taken away in the crop, for rendering the 

 exhausted soil fit for another crop of the same kind. 

 In a state of nature, on the contrary, the plants of 

 each piece of ground die where they grow, and by 

 decay give back to the soil what they took from it. 



30. The above-mentioned plant-foods are all 

 inorganic substances ; and until quite recently plants 

 (except fungi and parasites) have been supposed to be 

 incapable of deriving nourishment from organic sub- 

 stances except these be completely decayed. It is 

 now, however, ascertained that some plants can derive 

 nourishment from raw meat, insects, and other animal 

 and even vegetable matter, such plants being provided 

 with organs for the purpose of digesting such matters. 

 The leaves of the nepenthes, side-saddle flower, 

 venus's fly-trap, and sundew, are instances. In all 



