THE MANGROVE FAMILY 53 



which the tree grows is moist, but salt. If the tree were to absorb 

 a large quantity of salt, the vessels in both root and stem would be 

 clogged by salt, which would cause the death of the tree. The 

 tree must, therefore, reduce the quantity of water taken in by the 

 roots to a minimum, which is effected by diminishing the action 

 of transpiration. The water absorbed is thus not freely transpired, 

 but retained by the leaves, and the percentage of salt is kept at 

 a low rate. 



The diminution of the flow of the sap is required for a second 

 reason. Breezes are constantly blowing on the sea-coast. (The 

 heat of the sun's rays warms the land much more than the sea, 

 then the hot air on the land rises, and the cool air from the sea 

 rushes in to replace it. That is the ordinary sea-breeze by day. 

 The reverse takes place at night. The land cools down much 

 sooner than the sea, the warm air over the sea rises and is replaced 

 by a stream of air from the land, which we call land-breeze.) 

 A plant like the Mangrove tree that is thus constantly exposed 

 to winds is likely to wither easily and, hence, must be protected 

 against tA^r g^-eat a loss of water by transpiration. 



3. Routing in the muddy soil. — The soil in Avhich the Mangrove 

 grows is loose- and muddy, and the tides continually shake the 

 plant. The plant has to meet these unfavourable circumstances 

 and is for this purpose admirably provided. It sends out from 

 its trunk numerous horizontal adventitious roots which by means 

 of vertical shoots manage to get a Arm hold in the soft mud. 

 Such adventitious roots spring even from the branches. Mangrove 

 swamps thus obtain a peculiar appearance, especially at low-tide, 

 when the whole grove seems to be lifted over the water, as if 

 standing on stilts, or looks like so many spiders standing on their 

 long legs (fig. 56). The w^ater can now flow to and fro under 

 the trunks, just as under the piles of a pier, the stems remaining 

 firm . 



4. Germination of the Seed. — But what happens with the seedV 

 Is it possible for the germinating seed to take root in such an 

 unsteady soil as the beach affords? Provision is made also for 

 this difiiculty. Seeds, as a rule, take a long rest before they 

 germinate. The seed of the Mangrove tree, however, is an exception 



