Moisture Retention in Leaves of Conifers of the Northern Rocky Mountains

Leaves of ponderosa pine (Pinus ponderosa) retained more moisture when attached to cut branches than did those of Douglas fir (Pseudotsuga taxifolia), western white pine (Pinus monticola), arborvitae (Thuja plicata), grand fir (Abies grandis), or Engelmann spruce (Picea engelmanni). 2. Leaves of Douglas fir and ponderosa pine retained a higher moisture content on the average than did those of arborvitae, white pine, Engelmann spruce, or grand fir when the leaves were removed from the branches and allowed to dry in the laboratory. 3. Cut leaves of arborvitae and white pine showed no significant differences in moisture retained, but cut leaves of both species retained more moisture than did leaves of grand fir or spruce. 4. If the tetrazolium test is a test of relative viability, it did not indicate any results to substantiate the claim that the more drought-resistant coniferous species are better able to recover from a low content of leaf moisture than are those less drought-resistant. In general, a loss of leaf moisture below 50% on the basis of dry weight, and remaining below this level for 3 days, resulted in no tetrazolium test when rehydrated. 5. Leaf shrinkage was closely associated with water loss and appeared to be most marked in the case of ponderosa pine, although this took place over a longer period of time than with Douglas fir, grand fir, or arborvitae.