LEAF-STRUCTURE AS RELATED TO ENVIRONMENT 
535 
Hesselman (23) brought out many important facts in his very de- 
tailed and quantitative work. Leaves formed in the stronger Hght of 
the forest in the spring developed more palisade than leaves that de- 
veloped later in the weaker light. The trees that had high light re- 
quirements, Betula. Fraxinus, produced sun-leaves, while the trees of 
low light requirements, Ouercus, Corylus, produced both sun and 
shade leav^es. The trees in the first group produced starch in all the 
leaves, while those in the latter group produced no starch in the inner- 
most leaves. Shade leaves make more starch than sun leaves of the 
same species when the light is equal. The production of starch de- 
creases from spring to summer in the forest more in sun plants than in 
shade plants. The respiration of sun plants is far greater than of 
shade plants. If the leaf surface is equal, transpiration increases with 
the amount of palisade. Sun plants in the sun transpire much more 
than shade plants in the shade. The work also contains good repre- 
sentations of ecological structures of plants. 
Bergen (4) compared the transpiration, color, size and the general 
structure of sun and shade leaves of the same individuals of the fol- 
lowing: Olea europea saliva Pistacia, Lentiscus, Quercus, Ilex, Rhamnus 
Alaternus. He found the ratio in thickness of sun leaves to shade 
leaves to be 1.5-3.7 to i. The sun leaves had thicker cuticle, more 
palisade, smaller air spaces, greater bundle development, 15 percent 
more stomata as determined by two observations, greater scaliness, 
darker color and smaller area. The greater transpiration in the sun 
leaves was due to their greater activity, because their larger stems and 
bundles transfer the water more quickly, and because the greater 
thickness of the leaves afforded a larger interior evaporating surface. 
In another article (5) Bergen compares the thickness and transpiration 
of new and old leaves. From the result of another study (6) he states 
that "it is undoubtedly a fact that the great majority of woody dicoty- 
ledons have leaves which when freely exposed to the sun are concave 
on the upper surface and that this concavity usually lessens or disap- 
pears in the case of much shaded leaves on the same plant." 
Oltmans (26) noted that the leaflets growing on the south periphery 
of Rohinia Pseudo-Acacia trees were concave, while those on the north 
periphery were flat. Wiesner (32) also observed that while the upper 
surface of peripheral leaves was concave, the leaves in the shade of the 
same tree were usually flat. 
Herriott (22) gives the frequency and violence of the wind and the 
