Chap. VI] EDAPHIC INFLUENCES IN THE TROPICS 409 



tion, and consequently the transpiration, is much more considerable 

 and more regular in humid sea-districts than in those with slight rain- 

 fall. Dense and frequently repeated cloudiness apparently represents the 

 most essential climatic condition for the occurrence of mangrove in the 

 tropics. 



Beyond the tropics the limits of the formation as a whole, and those 

 of its individual members, are chiefly determined by temperature : — 



The North-East limit of the Eastern Mangrove as a closed formation, 

 according to Warburg's observations, apparently lies in South Liu-kiu 



Fig. 230. Mangrove in Florida. Interior view. Rhizophora Mangle. From ' Garden and Forest.' 



(Iriomotte, 25 N.) ; Warburg has not seen tall mangrove further North. 

 Even there it is already impoverished and consists of only four species (Bru- 

 guiera gymnorrhiza, Rhizophora mucronata, Sonneratia acida, ? Avicennia 

 officinalis); in the form of isolated individuals. Rhizophora mucronata still 

 appears in South Japan (Kagoshima, 32 N.) as the most northerly repre- 

 sentative of the Eastern Mangrove flora. In a South-East direction the 

 mangrove continues to the tropic of Capricorn in undiminished luxuriance, 

 but becomes lower in stature and poorer in species on the coast of New South 

 Wales (Avicennia officinalis, Aegiceras). Bushes of Avicennia occur even 

 in New Zealand and as far as Chatham Island (44° S.). The North-West 

 limit of the mixed mangrove lies at the mouth of the Indus ; beyond this 



