IB 

 caniiot ke^p uyj witli root pressure. Then the air spaces become 

 injected, and plant work cannot be carried oiit. 



2. The second danger is that of freezing. Plants best adapted 

 to cold are those which dry up during the winter, as Algae. The 

 drying up prevents freezing, hence many trees can live in cold regions, 



Too little water . 

 This is the greatest danger in plant life. 



1. Water is not a more important factor ecologically than food 

 or light, but a more variable one since many plants are exposed to 

 conditions varying from moisture to drought. 



2. It is not the absolute amount of water which determines whether 

 a plant may live in a certain habitat or not. If a pond contained 

 water for eleven months and dried up during one month, its vegetation 

 would be determined bjr the one month of drought. 



Xerophytes are plants that have adapted themselves to dry 



conditions. Xerophytes may grow in the water, yet have all the 



Warming 

 characteristics of desert plants. According tOj^Xerophytes are 



plants adapted to dry conditions only. Sehimper regards them as 



plants protected against excessive transpiration. 



Prrnups pf climatic Xerophvtes. 



1. Plants of the desert are Xerophytes in their highest and best 

 state, 



2. Mountain plants. 



3. Arctic plants. 



4. Plants of beach and sand dune. 



