52 DICOTYLEDONS 



all times of the year. There is plenty of water for every plant 

 during the rainy season, but hardly any during the hot season. 

 Again, plants with long and deep roots, such as large trees, can 

 draw water even during the rainless season from springs hidden 

 deep below, whereas many small plants with short roots cannot 

 reach any such reservoir. 



Plants that have a rich supply of water at their disposal, 

 therefore, generally possess certain arrangements in the structure 

 of their leaves and stems to facilitate the transpiration of water 

 at their surface, that is to say, their structure is liygrophilons'^ 

 (see " Helps to promote Transpiration" in II. Part). I)ut such 

 plants as have only a scanty supply of water must be very frugal 

 with it, they must reduce the process of transpiration toaminimnm 

 and their structure is said to be xerophilous^"'^ (see "Means to check 

 too much Transpiration" in II. Part). Plants that are able to 

 adapt themselves to various conditions as regards the supply of 

 water in the different seasons are said to be tropophilousy (see 

 Teak Tree). 



2. Xerophilous structure of the Mangrove. — If wej^^mine the 

 leaves of a Mangrove tree, e. g., Rhizopliora niucr(k'mfS; under a 

 microscope, we find that they are covered witMp" thick coat, 

 called the cuticle, preventing the evaporation of water accumulated 

 in tlie cells of the epidermis. We further find that there are a 

 number of additional layers of cells filled with water below the 

 epidermis of tlie upper side of the leaf w^hich may be said to be a 

 reservoir of water- The stomata are deeply set in the epidermis. 

 Many of the interior cells contain a slimy substance The leaves 

 of the tree liave a decidedly xerophilous structure like so many 

 plants growing in dry places. 



At iii'st sight, this fact must cause some surprise to the 

 observer; for tlie Mangrove tree lives on moist soil, and we should, 

 therefore, expect ahygrophilous rather than a xerophilous structure. 

 However, if we think a])out it a little more, we understand that 

 the Mangrove must necessarily be thus ('([uii)[)e(l. The soil in 



* From Urock hyyros, wet; .'iiid itliilos, lovin-,^. *'=Froiu Greek xeros. drj; 



and iihilos, lovin^^. f From Uro.'ik Irnpos, a turn. 



