174 



at it, finds it a synonym for his hopes 

 and speaks of "the tree of Hfc." 



The tree accomphshcs its increase 

 of stature and wider reach by means 

 of buds and soft, expansible tissue at 

 its extremities. When these tender ex- 

 tensions grow older they harden into 

 wood, and then the terminal buds 

 spring forth again to add to the annual 

 growth. 



While a tree agrees with bone in 

 the way of adding girth, and differs 

 from it in procedure at the end of the 

 branches, the roots face a different set 

 of circumstances. A root has to push 

 its way continually through rock and 

 sand and hard impacted earth, and yet 

 it must achieve this growth by means 

 of soft and tender tissues that make 

 such rough contact impossible. In this 

 case there is developed, on the end of 

 the growing tissue, a tough, hard 

 growing-cap consisting of cells that 

 have differentiated in this way, and 

 these serve to protect the cells behind 

 and plough the way for them. The 

 growth therefore takes place in a region 

 a short distance from the end. 



Ill 



A tree, like other forms of life, is 

 engaged in the constant circulation of 

 fluid through its tissues. Life processes, 

 animal or vegetable, can go on only so 

 long as each individual cell is sur- 

 rounded by a fluid containing nutri- 

 ment. To meet this demand and to 

 provide for a large amount of evapora- 

 tion, a tree passes up a great deal of 

 water. A fairly large beech tree will use 

 about sixty-five gallons of water on a 

 dry, hot day, while a large oak will re- 

 quire much more. And this water, in 

 the larger species of trees, will have to 

 be lifted two hundred and even three 

 hundred feet. 



Anyone who is familiar with pres- 

 sures in a tall standpipc or water tower, 

 or who has even taken up the problem 



FORESTRY 



of raising water to the second story of 

 a country residence, must be interested 

 in asking. How is this supply of water 

 taken to the top of such tall trees? 

 lliis question, in the present stage of 

 man's knowledge of physics, cannot 

 be answered. We do not know. 



I dare say that anyone with an 

 everyday knowledge of physics, such as 

 might be learned from a lamp wick, 

 would be able to suggest wa}s and 

 means of getting the water up there; 

 but it would be difficult to think of 

 anything that has not already been con- 

 sidered and found wanting. The lamp- 

 wick principle, capilhm' attraction, 

 will not go far in raising water. Water 

 rises in a capillar}' or fine tube to a 

 height in proportion to the fineness of 

 the tube; and the viscosity of water is 

 such that if the tube is very fine it 

 would not raise water to the top of 

 even a moderate-sized tree. 



Root pressure or osmosis has been 

 taken into consideration. By cutting 

 off a plant near the ground and fasten- 

 ing a glass tube upright on the stem, 

 it is possible to ascertain the height to 

 which its sap will rise by pressure from 

 below. Under favorable conditions a 

 grapevine will exert a pressure sufficient 

 to raise a column 36.5 feet, while a 

 birch has tested as high as 84.7 feet. 

 This might seem a promising line of 

 inquiry were it not that root pressure 

 takes place in woody plants onlv in 

 early spring, and especially in ' the 

 morning. It has been found that when 

 the tree is evaporating the greatest 

 quantities of water, on dry, hot da)'s of 

 summer, there is no root pressure what- 

 ever. This fact, once it was established, 

 naturally set root pressure aside and 

 left the problem unsolved. 



It has been proved beyond question 

 that the rise of water in the tubes of a 

 tree is caused by a pull from above. 

 That there is a strong pull upward can 

 be demonstrated by means of any 

 branch taken from a growing plant. 



