370 E. E. GAERTNER 



short-leaf pine absorbed more water from the soil than loblolly pine and 

 at the same time maintained higher total water content in its leaves even 

 when soil moisture was Hmiting. Short-leaf pine also maintained a higher 

 solute concentration when recovering froni the effect of drought; that is 

 when 30% soil moisture was restored. Schopmeyer's data indicate that the 

 greater drought resistance of short-leaf pine cannot be attributed to an 

 abihty to conserve water either by retarding transpiration or by forming 

 bound water, or having a higher osmotic pressure. Yet the rate of trans- 

 piration of loblolly pine gradually diminished over a period of six weeks 

 as decreased soil moisture approached and passed the 'wilting coefficient'. 

 At the end of six weeks the transpiration rate was only 16% of that at 30% 

 soil moisture. This does not agree with Veihmeyer and Hendrickson's 

 (1936) data on fruit trees. Wilhelmi (1957) presented terminal growth data 

 of young broad-leaved and coniferous trees growing on irrigated and 

 control plots. His best species included Popiihis angiilata and Salix purpurea, 

 both considered suitable for dry sites, but both growing better on the 

 irrigated site. Young conifers growing in the Rocky Mountains at low 

 altitudes stand the lack of growth water for longer periods and their roots 

 have a more rapid rate of penetration than those trees growing at high 

 altitudes (Daubenmire, 1943). 



Lyon (1940, 1943) has studied the correlation of growth with seasonal 

 rains and temperature in various conifers as well as red oak [Quercus borealis 

 Michx.) ; only in red oak was there no correlation between the rain of the 

 previous season and growth, though some effect of rains falling during the 

 growing season was noted. His conclusions stressed the effect of variation 

 of water supply on radial growth fluctuations. He found that white pine 

 growth is sensitive to water supplied by rainfall. In white pine, terminal 

 growth of the primary and secondary axes had the closest correlation with 

 the amount of rainfall from the 'storage' May-November season of the 

 preceding calendar year (Motley, 1949). Red pine did not show the same 

 correlation but perhaps the material was too young and not yet estabhshed. 

 Since food used for apical growth is manufactured the previous year 

 (Kienholz, 1934; Kozlowski and Ward, 1957), one would expect apical 

 growth to be correlated with the preceding summer's rainfall when the 

 efficiency of photosynthesis could be affected by abnormal weather con- 

 ditions. This is especially true in the temperate regions where an adequate 

 supply of soil moisture is usually available from melting snows in spring 

 and early summer when growth first occurs. Growth-rainfall trends in six 

 species of hardwoods were studied by Friesner (1950) to obtain a growth- 

 rainfall trend coefficient. He found a definite correlation between rainfall 



