THE ASCENDING SAP 



93 



purpose. One organ pumps up the re- 

 quired water, another carries it, another 

 uses it in cooking, another gets rid of the 

 waste, another obtains the solid food, another 

 carries the cooked provisions to all parts of 

 the structure, another stores up the super- 

 fluity, another builds additions to the edifice, 

 while another prepares to send out a colony 

 furnished with supplies of food, and with 

 everything requisite to begin life for them- 

 selves " (Carpenter). This is very true ; 

 and we propose now to treat a little of 

 some of these interesting functions, on the 

 discharge of which depends not only the life 

 of the plant as a whole, but the permanence 

 of the species. 



Now, all the operations carried on in a 

 plant are subordinate to the two great 

 functions of nutrition and reproduction 

 nutrition, by means of which the life of 

 each individual is sustained ; and repro- 

 duction, which secures the continuance of 

 the species. For the present our remarks 

 will be confined to the former. 



We may enter upon the subject at once 

 by asking, What is the food of plants ? a 

 question which involves the further inquiry, 

 What are the constituents of protoplasm ? 

 For if, as we have seen, all vegetable cells 

 originate in protoplasm, and every plant 

 consists either of a cell or cells, or the pro- 

 ducts of their formation and transformation, 

 it stands to reason that the elements of 

 protoplasm must constitute a very large 

 proportion of the food of plants. Now, the 

 chief elements of protoplasm have been 

 already enumerated. They are six in num- 

 ber carbon, hydrogen, oxygen, nitrogen, 

 phosphorus, and sulphur; but in order to 

 complete the list of nutrient substances, 

 we must add the elements iron, calcium, 

 potassium, magnesium, zinc, and, probably, 

 sodium and chlorine. 



Of these elements carbon is by far the 



FIG. 125. FIRST YEAR OF NORFOLK 



OR FOUR-COURSE ROTATION OF 



CROPS. 



FIG. 126. SECOND YEAR OF NOR- 

 FOLK OR FOUR-COURSE ROTATION 

 OF CROPS. 



