PHYSIOLOGY OF THE RED MANGROVE. 615 



The Leaf. 



It is in the leaf that a great many of the adaptations of the man- 

 grove to its special environment are seen. The leaves, as mentioned 

 before, are opposite and assume somewhat a perpendicular posi- 

 tion. Johow^^ regards this position as a protection against the light, 

 the great intensity of which has, according to him, a destructive 

 effect on the chlorophyll. Each pair of leaves is provided with two 

 interpetiolar stipules which are twisted in the opposite direction 

 from that of the leaf which it encloses. The unfolding of the leaf 

 blade from the stipule occurs as in the figs. The stipules are pro- 

 vided with glandular hairs, which secrete a resin-like substance that 

 Eggers^" says covers the plumule in the seedling stage and protects 

 it against the action of the water when the seedling floats in the sea. 



Warming'^^ figures a diagram of the cross section of a petiole 

 in which there is a ring of vascular tissue and inside this ring are 

 several other vascular bundles with the phloem turned in the reverse 

 direction. In his opinion these strands arose as splits from the 

 bundles on the upper side. 



The leaf blade is elliptic and has a very prominent midrib, as 

 Sloan"* observed in his early description. The epidermis is very 

 heavily cutinized, especially on the upper side which entirely lacks 

 stomata (Fig. 3, PI. V.). The stomata are slightly sunken and 

 provided with an antechamber (Fig. 4, PI. V.). According to 

 Warming the stomata originate at different times, the younger be- 

 tween the older ones, and are scattered in every direction. A most 

 striking feature of the leaf tissue is the large, mostly four-celled 

 water-storage hypodermis. This is a true hypodermis, as may be 

 seen in examining young leaves still rolled in the stipules, which 

 even here show a number of layers of these cells. The upper 

 layer of the hypodermis or mostly the two uppermost layers are 

 filled with tannin (Fig. 5, PI. V.). The function of these tannin 



'1 Johow, Fr., loc. cit., p. 419. 



"- Eggers, H., " Rhizophora mangle L., Videnskabelige, Meddelelser," p. 

 180, 1887. 



'3 Warming, Eug., " Rhizophora mangle L., Tropische Fragments," II., 

 Engler's Botanisehe Jahrhuchcr fur Systematik, Bd. 4, 1883, p. 319. 



'* Sloan, H., " A Voyage to the Island Madeira, Barbados, Jamaica, etc.," 

 1725- 



