Varying Structure of Conifer Leaves in Different Habitats

1. In the mesic habitats of the two altitudes in the Medicine Bow Mountains investigated, the needles of Abies lasiocarpa were found to be longest, widest, and thinnest; those of Picea engelmanni longest and with the smallest cross-section; and those of Pinus contorta larger in all dimensions than those from the xeric habitats of the Laramie Range. 2. Thickness of the cuticle increases with age of the leaves; it is thickest in the xeric habitats and in the bright sunlight of the alpine habitat. Thickness of the walls of the epidermal cells varies in the same way. 3. The stomatal pits tend to be deeper in the older leaves and the leaves from xeric habitats on the fir and spruce; there is little variation in their depth on the pine. 4. The number of cells in the hypodermal sclerenchyma is greater in older leaves, and the greatest number is found in the leaves from xeric habitats. 5. The ceils of the mesophyll in all three species are more compact in the older leaves and most compact and with the smallest intercellular spaces in the leaves of trees from xeric habitats. The thickest cell walls and their greatest lignification occur in the leaves from xeric habitats. The resin ducts of largest diameter were found in the leaves from xeric habitats. 6. There is an increase in the size of the veins and in the number of ceils of the veins in each species by the growth of cambium. The greatest increase in number occurs in the phloem. Most cambium growth is in the pine. 7. The oldest leaves are found in the trees growing in the mesic habitats. The oldest needles on the wind-blown trees of the high alpine flats are on their lee side