WATER UTILIZATION BY TREES 9 



Friedrich (60) found that the water content of wood at about 6:15 

 p. m. was about 52 percent. Early the next morning it was about 

 56, and at noon on the same day about 51 percent. This difference 

 of 5 percent between the water content in the early morning and at 

 noon is explained by the water losses during the daytime, as will be 

 discussed later. Doubtless the increase in the amount during the 

 night serves to replenish the loss of the previous and following days. 

 This effect may be important, since a 5-percent reduction of the water 

 content of a stand running 100 M board feet to the acre would equal 

 about one-seventh of an inch of rainfall, as calculated by Baker (6). 



The moisture content of wood varies also with the height in the 

 tree as indicated by Luxford (141), who noted that in redwood, espe- 

 cially in the heartwood, there was a marked decrease in the water con- 

 tent with height up to about 80 feet, when the decrease in water con- 

 tent became much more gradual. Sap wood, on the other hand, 

 although containing much more water than the heartwood, seemed to 

 increase only slightly in water content at the higher levels, the net 

 result being a decrease of about 15 percent per entire cross section 

 between the top and bottom of the tree. Huckenpahler (111), how- 

 ever, working with shortleaf pine in North Carolina, found that the 

 moisture content in an entire cross section (in summer) increased 

 upwards from about 80 percent of the dry weight at 1 foot above the 

 ground to about 175 percent at 25 feet. The water content of the 

 phloem changed very little with height, but the wood, especially the 

 sapwood (outer two rings) increased from 100 percent at the 1-foot 

 level to 185 percent at the 25-foot level. Both workers are agreed, 

 however, on the fact that the heartwood decreases decidedly in water 

 content from the base upward. The total amount of water in a tree 

 may thus reach a very large figure; in a redwood 5 feet in diameter 

 and 200 feet high Luxford calculated that there are about 17 tons of 

 water. 



Drought periods are reflected in the moisture content of the wood, 

 as shown by Beilmann (12), who found that in the vicinity of St. Louis 

 the unusual seasonal distribution of the rainfall in 1932-34 ultimately 

 resulted in severe wilting or total defoliation in July 1934, accompanied 

 by changes in the wood-moisture content, as measured in borings from 

 about 25 different species. The moisture content averaged about 50 

 percent of the wood. The higher the water content the better were 

 the trees. Those trees with less than 50-percent moisture content 

 (July 19-22, 1934) were either seriously wilted or completely defoliated. 

 In agreement with other workers Beilmann (12) found that trees of 

 similar apparent condition may vary as much as 5 percent in their 

 wood-moisture content. 



OSMOTIC PRESSURE MEASUREMENTS 



In the studies just described, the water content has been measured 

 on a dry- or fresh- weight basis. In the living cells of the tree, water 

 content is important, however, not only from the point of view of 

 absolute amounts present, but also from the point of view of the propor- 

 tion of osmotically active substances that the cell sap may contain 

 in solution. This determines the osmotic pressure of the cell, which, 

 in turn, determines the ability of the cell to take in water from the out- 

 side or to pass it on to other cells. Numerous studies have been 



