ENVIRONMENT 101 



conditions for some years back. Thus, during the dry period from 

 1870 to 1905 or so, the trees responded each year to the fluctuations 

 in rainfall, but with less and less spirit. This suggested that the con- 

 servation was in the tree itself. 



Reversed conservation — In considering the details of smoothing 

 curves of tree-growth (page 44), it seemed as if the derived value should 

 substitute for the last of the several used in getting it, but as a matter 

 of fact there appeared to be better agreement with rainfall when the 

 derived value was placed in the middle, as in the graphic Hann, used 

 so much in the western groups. This could only be true if favorable 

 years affect the preceding year as well as the one after. And in the 

 growth of trees that is not impossible, so far as we know at present, 

 as will appear in the next topic. 



Possible change in ring-size — The sapwood commonly holds much 

 reserve moisture which can without doubt be drawn on for the needs 

 of the tree and whose depletion can be changed to abundance when 

 conditions are favorable. It may be that the conservation or vitality 

 of the tree lies in this storage capacity. If so, it is entirely conceivable 

 that the moisture condition of the growing layer affects the actual 

 size of the rings near it, and that the ring-size is not absolutely fixed 

 for several years after its growth. A first attempt to test this matter 

 by borings in the same tree (FL-90) at 4-year intervals was not satis- 

 factory, because the cores happened to show some slight irregularities 

 in growth and were allowed to dry before measurement. Such varia- 

 tions as are referred to here might show in the dendrograph.* 



Water-soaked rings — As an illustration of probable change in 

 ring-size in dead trees from excessive water-content, reference is here 

 made to the tests on a fallen sequoia described on page 24. 



Repeated use of rain — Somewhat connected with the subject of 

 conservation is the matter of the repeated use of rain. In separating 

 the rainfall at Prescott into winter and summer records, the cycles of 

 the winter rains at Prescott seem to be repeated in the summer rains, 

 but the important ones in the summer rains do not carry over to the 

 winter. This seems to mean that winter moisture lasts over locally to 

 summer, but summer moisture mostly runs off or evaporates. This 

 difference comes from the different types of storms in winter and 

 summer. In the former, the storms come from the coast and clouds 

 are continuous over an immense area. There is no chance for evapora- 

 tion of any amount. On the other hand, in summer the sun is very 

 powerful and each morning promotes evaporation over large areas 

 between the scattered clouds. Storms come from the south and con- 



*Since the above was written, Dr. MacDougal has told me that he has detected with the 

 dendrograph certain changes in the thickness of the two or three outer annual rings, depending 

 on the temporary condition of the moisture-supply. 



