146 TRANSACTIONS OF THE ILLINOIS 



After investigating the wonderful development of the root sys- 

 tem of plants, we may not be greatly surprised when we find that the 

 amount of water which a vigorous plant, under favorable circum- 

 stances, takes from moist soil is a very large quantity. Here again, 

 however, the truth far exceeds popular estimates. It has been shown 

 by abundant experiment that, upon an average, ordinary thin-leaved 

 plants give off each fair summer day one and one-fourth ounces of 

 water for each square foot of leaf surface. This comes entirely from 

 the soil through the roots. The amount as now expressed may not 

 seem large, but when we take account of the entire leaf surface, we 

 at once reach astonishing results. A large-sized forest tree has 200,- 

 000 square feet of foliage surface. Applying our data, we find the 

 incredible amount of forty barrels of forty gallons each. Ten such 

 trees may stand on an acre — 400 barrels, in fair w^eather daily, of 

 water exhaled ! I say incredible. This is the inevitable expression 

 of every one upon first announcement. But while no one has proved 

 the fact in regard to a large tree by direct means, the often repeated 

 results with numerous kinds of potted plants amply justify the con- 

 clusion just expressed. When we come to reduce the 400 barrels to 

 a layer spread over an acre of surface, the fact does not appear so 

 unreasonable, since such a structure would be little more than one- 

 twentieth of an inch in thickness — an amount much less than would 

 escape from the exposed surface of water itself by evaporation. 

 Careful experiments upon sugar beets in France gave eighty barrels 

 of water per acre as the daily average of transpiration of water. 

 Our corn-fields in full development must nearly or quite equal 

 forest areas of the same size in the amount of water absorbed from 

 the soil. 



A less practical, but not less interesting, topic is the force by 

 which roots send upward the absorbed water. This force is not ap- 

 parent in plants furnished with leaves, because the water in such 

 cases does not accumulate in the tissues sufficiently to permit the 

 pressure to be exercised. But in spring-time, before the buds swell, 

 or at any time, if the top is removed the continued absorption by the 

 roots fills the tissues to overflowing, and what is called bleeding oc- 

 curs. The flow of "sap" from the maple tree is of the same char- 

 acter. Now, if a gauge is placed upon a stump having active roots, 

 in such way as to measure the pressure of the exuding water, re- 

 markable results are obtained. In the experiments upon the squash 

 vine at iVmherst, Mass., it was found that such gauges indicated a 

 pressure sufficient to sustain a column of water forty-eight feet high. 

 At the same place a birch tree gave a pressure equal to eighty-four 

 feet of water — nearly three times the weight of the atmosphere. We 

 cannot doubt that the roots of trees are capable of forcing water to 

 the tops of the tallest monarchs of the forest.- This is explainable 

 by reference to the same molecular attractions heretofore described. 



