654 BOWMAN— ECOLOGY AND 



phora has been described in detail in the chapter on morphology, 

 but several studies were made on the leaves to learn to what extent 

 the adaptation is carried in different habitats, or rather media of 

 growth. To this end then, leaves were secured from trees growing 

 in fresh water along the Miami River, from trees growing in pure 

 salt water off shore in the Atlantic, northeast of Miami, and also 

 from trees growing in the rather dry situations in the Marquesas 

 atoll in the Gulf of Mexico, in soil only reached by the highest tides 

 and in the same atoll, of trees growing off shore in salt water several 

 feet deep. Sections were made of these leaves in various prepara- 

 tions, free hand, of fresh and pickled material, and also paraffine 

 preparations, and comparisons made of the thicknesses of the leaves 

 and the relative amounts and positions of the various tissues in the 

 leaf. Drawings and microphotographs were made and are here 

 given. In each of the two sets of preparations leaves were selected 

 of the same dimensions and at about the same node back from 

 the bud so that the compared leaves were as nearly alike as could 

 be possible. As a rule, however, the leaves on trees in fresh water 

 w'ere slightly larger than those for the corresponding node in salt 

 water trees. In Fig. 2, PI. VII., is seen the illustration of the fresh 

 water section. It will be noticed that the tannin cells of the hypo- 

 dermis are shorter and rounder, the water storage cells are smaller 

 and only in two rows, the palisade is thicker and the spongy 

 parenchym not so deep and the stomata slightly larger than the 

 corresponding features in the salt-water leaf section shown in Fig. 

 I, PI. VII. The greatest difference seems to be in the amount of 

 water storage tissue and the lengths of the palisade cells. In the 

 salt-water leaf the palisade lies almost in the middle of the leaf, and 

 the tannin cells are also rather larger and elongated ; this detail also 

 helps to strengthen the writer's view regarding the function of these 

 layers of cells as insulation against the heat and light. The ranker 

 growth of the river bank mixed with other trees help to make more 

 shade for the trees in this situation. The sections of the inshore 

 leaves, and the offshore leaves show much the same relation on a com- 

 parison of the sections, but in a less striking degree. The offshore leaf 

 (Fig. 4, PI. VII.) is the thicker, i. e., showing a typical halophytic 

 reaction, while the inshore leaf (Fig. 3, PI. MI.) is slightly thinner. 



