96 



PLANTS 



by a process analogous to digestion and absorption securing 

 in this way the requisite nitrogenous matter. Such carnivorous 

 plants are found in soils or situations which are in an unusual 

 degree devoid of nitrogenous compounds of all kinds. 



Physiographic Relations 



219. Finally we may note briefly the physiographic relations 

 of plants. From geological evidence we know that vegetation 



Fig. 51. — The Venus fly-trap closed, showing interlocking teeth. 



has existed upon the earth for vast ages and has undergone 

 continual changes with the lapse of time. Long before the 

 advent of man, vegetation flourished as it has not done since, 

 and in certain regions of the earth's surface the remains of 

 those early forests accumulated to such an extent as to form 



