. Research methods in ecology. Plant ecology. 181. Types of leaves. Isophotic leaves are equally illuminated and possess more or less uniform chlorenchym. Diphotic leaves are unequally illuminated, and exhibit a differentiation into palisade and sponge tissues. They may be distinguished as isophotophylls and diphotophylls respec- tively.^ Isophotic leaves fall into three types based upon the intensity of the light. The staurophyll, or palisade leaf, is a sun type in which the equal illumination is due to the upright position or to the reflection from a light soil, and in which the chlor- enchy
. Research methods in ecology. Plant ecology. 181. Types of leaves. Isophotic leaves are equally illuminated and possess more or less uniform chlorenchym. Diphotic leaves are unequally illuminated, and exhibit a differentiation into palisade and sponge tissues. They may be distinguished as isophotophylls and diphotophylls respec- tively.^ Isophotic leaves fall into three types based upon the intensity of the light. The staurophyll, or palisade leaf, is a sun type in which the equal illumination is due to the upright position or to the reflection from a light soil, and in which the chlor- enchym consists wholly of rows of palisade cells. The diplophyll is a special form of this type in which the intense light does not penetrate to the middle of the leaf, thus re- sulting in a central sponge tissue, or water- storage tissue. The spongophyll, or sponge leaf, is regularly a shade type; the chlor- enchym consists of sponge cells alone. For the present at least it is also necessary to refer to this group those monocotyledons which grow in the sun but contain no pali- sade tissue. Diphotic leaves always contain both palisade and sponge, though the ratio between .them varies considerably. Diphot- ophylls are characteristic of sunny mesophytic habitats. They are frequent in xerophytic habi- tats as well as in woodlands where the light is not too diffuse. In the case of stable species, this type of structure sometimes persists in the dif- fuse light of coniferous forests. Floating leaves, in which the light is almost completely cut off 'frorn the lower surface, are also members of this group. Submerged leaves, on the other hand, are spongophylls. 182. Heliophytes and sciophytes. The great majority of sun plants possess diphotophylls. This type is represented by Pedicularis procera 'Clements, E. S. The Relation of Leaf Structure to Physical Factors. 1905. Fig. 44. A stable species Erigeron speciosus: 1, sun leaf; 2 shade leaf (light .03). X Please note that these images
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