the wood, although one is formed in 

 each for every season that the tree 

 lives. 



The roots of the tree spread out un- 

 derground and are the agents through 

 which the tree derives most of the 

 moisture so necessary to its growth. 

 They absorb moisture only at their 

 extremities and usually spread to just 

 such an extent that the water which 

 falls off the outer branches of a tree 

 during a rain, falls exactly where the 

 tender rootlets can gather it up at 

 once and hurry it back up the trunk 

 of the tree. In ground that is springy, 

 or naturally moist, the roots do not 

 depend so much on the rainfall but 

 reach out after moisture wherever it 

 exists in the soil. 



Spring seems to give a new impulse 

 to life, especially to vegetable life, 

 which always responds promptly to the 

 genial rays of the sun. During the 

 winter, in our climate, the cells which 

 form our trees are contracted by the 

 cold and when the warm days cause 

 them to resume their natural size, a 

 small vacuum is formed in each cell, 

 which the first warm days proceed to 

 enlarge by thawing only the trunk and 

 branches of the tree, leaving the roots 

 below embedded in frozen soil from 

 which but little moisture can be drawn, 

 while evaporation draws moisture from 

 the trunk and branches with irresistible 

 force. A warm rain now comes, thaws 

 out the soil, and sets the juices therein 

 contained in motion. An immediate 

 rush of sap up the trunk of the tree is 

 the result. It clears out the pores or 

 channels, as a spring freshet clears 

 out the water courses, it rushes into 

 the branches, and the branches re- 

 joice and put on their livery of 

 green; it rushes out through the por- 

 ous surface of the limbs and rises in 

 the air in the form of vapor, while that 

 which does not escape becomes charged 

 with life and returns down a devious 

 pathway and lays the foundation for 

 another season's growth. 



But why should the sap ascend the 

 tree? 



This is only one of many questions 

 that the tree will not answer and no 

 one else ever has answered. If we take 

 a strip of blotting-paper and insert one 



end of it in an ink-well, the ink imme- 

 diately begins to climb up the blotting- 

 paper by means of the force known as 

 capillary attraction. Here, says the 

 seeker for truth, is the reason for the 

 ascent of sap, and many profound au- 

 thors have agreed that he is right. 

 Others claim, however, that he is 

 wrong, while still others think he is 

 only partly wrong and that this force 

 has something to do with it. If we cut 

 the roots from a tree and insert the 

 stem in water we will soon find that 

 this force is not the sole cause for the 

 ascent of sap. Another student has 

 made experiments with the force called 

 diffusion, and claims that this explains 

 the rise of sap to such remarkable 

 heights; but diffusion does not work 

 fast enough and hence must be thrown 

 aside. Another finds that water is im- 

 bibed through fine porous substances 

 with great force and that air can thus 

 be compressed to several atmospheres, 

 and this force is affirmed to be the 

 one at work in our trees. But the fact 

 that the amputation of the leaves and 

 branches checks the ascent is brought 

 forward and this theory falls to the 

 ground. The fact that liquid films 

 have a tendency to expand rapidly on 

 wetable surfaces was next advanced, 

 but the objection to the first theory 

 met it at once. 



Another interesting theory is now 

 brought forward and has the advantage 

 of practical demonstration, that is, an 

 artificial model was made through 

 which water ascended. It is based on 

 the principle that water will pass 

 through moist films that air will not 

 penetrate, on the fact that evaporation 

 takes place under right conditions 

 with force enough to cause something 

 of a vacuum, and also on the elasticity 

 of the cells. 



The model was constructed of glass 

 tubes, closed at one end with a piece of 

 bladder, and joined together in series 

 by means of thick-walled caoutchouc 

 tubing; the top which represented a 

 leaf was a funnel closed by a bladder. 

 This artificial cell chain was filled with 

 water, mixed with carbolic acid to 

 keep the pores from clogging, and was 

 set up with its base immersed. The 

 fluid evaporated through the membrane 



55 



