166 STATE POMOLOGICAL SOCIETY. 



THE CIRCULATION OF THE SAP 



is commonly given in the text books as a very simple matter which every 

 scbool-boy is expected to know and understand. Late researches indicate to 

 me that no one yet is able to give good and satisfactory reasons for all the 

 movements of sap in plants. 



At certain seasons of the year some plants are full of sap. If cnt or bruised 

 gome of it runs from the wound. A majority of plants, however, will never 

 run sap if they are tapped at any season. 



The sap in a maple tree in spring acts very much as though the bark were a 

 tight cylinder filled with water to the top. The materials dissolved in water, 

 and all taken in by the roots, are called the crude sap. This exists only in 

 theory, as it is at once more or less mixed with the assimilated sap. 



Field and garden plants absorb most of their nourishment through their 

 roots in the soil. 



Soil-water alone does not appear to contain all the materials necessary to 

 nourish plants, except in very rich soil. The leaves take in carbonic acid. 



Some plants thrive in damp air attached to trees which may be living or 

 dead. They receive their food in the form of air, vapor, or perhaps occasionally 

 as a liquid. 



Some of the higher plants which live in water may take their nourishment 

 through the leaves as well as through the roots. Some of the lower water 

 plants (sea weeds) absorb nourishment from the water by all their parts. This 

 of course must be the case with all our one-celled plants, which are quite nu- 

 merous in variety and large in numbers. 



. Johnson says agricultural plants take mostly A^^'roscojoic water through their 

 roots. That is a water which is not perceptible to the senses. 



Eice, willows, and many other plants take freely what is called bottom water, 

 or standing water. Some writers maintain that the passage of sap through 

 plants can be satisfactorily explained on mechanical principles alone, while 

 others as strongly maintain that it is still unexplained, and attribute the phe- 

 nomena to the vitality of the plant. 



Osmose is one of the mechanical principles usually urged to account for the 

 rise of sap to the leaves. This may be briefly stated as follows; When two 

 liquids or solutions are of different density, or have a difierent attraction for a 

 porous membrane which separates them, the liquids will usually each pass 

 through the membrane and soon mix with one another. Endosmosis " de- 

 pends upon the attraction of the membrane for the two liquids" (Dalton, p. 

 295). 



If water be one of the liquids and albumen the other substance, the water 

 will pass through the membrane to the albumen, but no albumen will pass in- 

 to the water. Other and more complete explanations are given already in 

 Dalton's Human Physiology. Capillary attraction is supposed to exert much 

 influence on the ascent of sap. This is an operation familiar to every one as 

 exhibited in the ascent of oil in the wick of a lamp. 



Unless the air is saturated with moisture much vapor is constantly passing 

 off through the leaves. This must aid in causing water to enter the roots. 

 Mr. Herbert Spencer has shown that the motion of plants, swaying to and fro 

 by the wind, is a great aid in causing sap to ascend; vet, sap gets up easily 

 enough though, when plants grow in perfectly still places. 



