THE MANGROVE OF THE BOMBAY PRESIDENCY. 655 



Especially well developed is the aqueous tissue in the old yellow 

 leaves of Rhizophora mucronata. The fact that these leaves are much 

 thicker and more fleshy than the green leaves of the same plant, is due 

 to the circumstance that those leaves which have become unfit for 

 further assimilation develop a large aqueous tissue, which serves for 

 some time as a water-reservoir. 



What we have observed in a few representatives of the mangrove 

 vegetation is equally applicable in some way or another to the rest. If 

 we consider all those structural peculiarities, we find that they belong 

 to the xerophilous type, i.e., they all are adaptations which help to 

 diminish the transpiration of the plant. Just for this reason the 

 mangrove is characterized by the extraordinarily thickened and cuticu- 

 larised walls of their epidermal cells, because these diminish the trans- 

 piration from the outer surface of the leaves. In the same direction 

 works the circumstance that the intercellular spaces in the mesophyll 

 are reduced. It is a striking fact that the intercellular spaces are 

 always larger where there is abundance of moisture than in places 

 where there is only little of it as, e.g., in deserts, on a rocky ground, 

 on sand or gravel. Plants growing on these substrata show in the same 

 way the other peculiarities of the mangrove, viz., lengthening of the 

 palisades, depression of the stomata, formation of aqueous tissue and 

 multiplication of the vascular bundles. This latter contrivance renders 

 the regular conduction of water to all parts of the tissue easier and is, at 

 the same time, a means for the removal of the prepared food-materials. 

 One would not think at first sight that the mangrove needed the 

 structural modifications which are so useful and even necessary for the 

 existence of those plants which grow in dry places. The mangrove sends 

 its roots deep down into the mud, its stems are washed by the water for 

 many hours of the day, and the branches and leaves are surrounded by a 

 moist atmosphere and, nevertheless, it exhibits all the anatomical peculi- 

 arities charaterizing those plants which are forced by circumstances to be 

 economical in the expenditure of their water. It is a general experience 

 that salts in solution render the osmotic absorption of water by the roots 

 difficult. These receive much more water if it is in a chemically pure 

 state than from solutions, and there is fixed for every plant a certain de- 

 gree of concentration, usually not exceeding 3 per cent, beyond which 

 absorption of water by the root does not take place any more. It is for 

 this reason that a substratum fermented by a rich salt solution is, with 



