56 THE STORY OF PLANT LIFE 



produced by a single plant, and the varying condi- 

 tions to which they are exposed, this is a natural 



Gymiiospermse 



Angiospermae 



Bryinese 



iSi 



Ase 



Isoetaceae 

 Filicinese 

 Leptosporangiatse 



Marsiliaceae 



Hepaticae 



conclusion. Each plant responds to the stimuli that 

 its habitat provides, and as the habitat and the other 

 factors such as soil and the variable degrees of heat, 

 light, moisture, etc., are variable it is not difficult to 



