2 Feeds and Feeding. 



potassium, calcium, magnesium, phosphorus, iron, chlorin and 

 sulfur. The plant can make no use of these elements in their 

 uncombined form, with the single exception of oxygen, of which 

 it may utilize a small amount in elementary form. All the other 

 elements, as well as oxygen for the most part, must be combined 

 with one another in some form to be of use to the plant. The 

 mineral substances which are taken up by the roots of the plant 

 may be grouped as follows: 



Sul fates ^ C Potassium 



Phosphates I * I Calcium 



Nitrates and | 1 Magnesium and 



Chlorids J [ Iron. 



Nitrogen in the form of nitrates and as ammonia is taken up 

 by the plant through its roots. Legumes (peas, clover, etc.) 

 possess the power of fixing the free nitrogen of the air through 

 the intermediate action of certain species of bacteria harbored 

 by the roots. Otherwise such 'nitrogen is not directly available 

 for plant growth. 



3. Water required by plants. Water, as we may judge from 

 its abundance in plants, is of the highest importance to them. 

 Half-grown clover plants may contain as much as 92 per cent, 

 water, or more than is found in skim milk. The turnip contains 

 from 87 to 92 per cent, water. When a crop of corn is partially 

 grown, nine-tenths of its whole weight may be water. Plants 

 exhale a large amount of water through their leaves during 

 growth. A sunflower plant 3.3 feet high has been known to 

 exhale 1.25 pounds of water through its leaves during twelve 

 hours. Lawes and Gilbert found in the moist climate of England, 

 that wheat, barley, beans, peas and clover exhaled during five 

 months of growth about 200 times their dry weight of water. King, 

 of the Wisconsin Station, l measuring the water given off through 

 leaf evaporation as well as by the soil supporting the plants, 

 found that for each pound of dry matter produced by the plant 

 in root, stem, leaf and seed, there were required for corn 301, 

 for barley 401, and for oats 501 pounds of water. The transpi- 

 ration of water by the leaves causes an upward progress of that 

 liquid from the roots through the stem of at least 1.3 inches 



1 Kept. 1891. 



