68 

 drainage. Few bacteria in swamps. Too acid to raise many plants. 



Forests — evergreen, tropical forests highest development of plant 

 kingdom. Richer the forest, greater the humls. Accumulative effects 

 in a forest. C. and M. are gradually increasing in a forest soil. 



(d) Mixed soil as loam — either humis or a mixture of two or three 

 elements known as mixed soils. 



(e) Calcareous soils. — marls of N.J. coral soils of P-errauda. 



(f) Salty sbils. Salt sbbbs to produce a xeropliytic form of plants. 



Chemistry vs. Phvslcs of Soils. 

 Which has more effect \xpon flora of the region ? Ahnxpt changes in 

 flora from one strat"^ to next. 



One theory, the chemical conditions of the soil.. linger. 

 Thurraari, on the contrary, held the view that the kind of soil 

 decides the flora, whether it is dry or porosis, etc. Warming 

 ■accepts the physical theory in most cases ; hut excepts halophytes 

 or marsh plants. Schimper inclines to the chemical view. Dr. Cowles 

 considers the chemical view the better. 



Mgell called attention to strugp-le for existence ; that 

 chestnut grows in sandy places not because it likes it best but 

 because the beech crowds it out by occupying better places. 



Another factor is the phvaio graphic age of region. The true 

 theory is probably that of a mixture of all four. 



