LIFE-HISTORY OF A TREE 67 



years; thus the roots become elongated, but in a different 

 manner from what occurs with the limbs. The new growth 

 of roots, as well as that of the buds, leaves, twigs, bark, etc., 

 of the stem, is furnished with food until the little hairs 

 can begin their work in the spring that had been stored 

 up in the cambium layer on the stem, limbs, and roots dur- 

 ing the late growth of the previous year, substantially the 

 same as food had been provided in the seed for the young 

 to subsist on until the leaves are developed and all the func- 

 tions of tree-life have become active. In order to protect 

 themselves from injury the roots, as well as stem and 

 branches, put on a coat of bark. 



The Sap. The circulation of the sap of a tree the water 

 with mineral food in solution gathered from the ground by 

 the little rootlets and carried upward and outward to the 

 extremity of the branches is more wonderful, more com- 

 plicated, and less understood than the circulation of the 

 blood in animals. In animal life the muscular heart liter- 

 ally pumps the blood through the arteries, at the same time 

 drawing it from the veins. In animals there are separate 

 channels for the circulation of the blood, one for the incoming 

 to the heart and the other for the outgoing ; but it is not 

 known, though it is probable, that some certain ones of the 

 pores or ducts in the wood of trees serve as passageways for 

 the sap and mineral food to the leaves and others for its 

 return to appropriate places after digestion. It is done in 

 some way, but we do not know just how ; possibly the di- 

 gested food is carried back through pores in the live bark. 

 Neither is there anything akin to a pump to be discovered 

 in a tree or other plant life. The roots take in water, and 

 by some unknown process, it climbs upward to the tops of 

 the tallest trees, apparently as easily as it does in a diminu- 

 tive plant. Redwood trees are frequently found three hun- 

 dred feet in height. A column of water that high will pro- 

 duce a pressure at the base of nearly one hundred and fifty 

 pounds to the square inch. Evidently there are resting- 

 places along the way, or something that shuts off the pres- 



