426 



VEGETATION OF THE CARBONIFEROUS PERIOD 



stem, whilst at b they are disposed in whorls, separated from one 

 another by more than the length of the leaf itself. 



Fig. 14. 



It may well be asked how the botanist can pronounce these dissimilar 

 forms to belong to one plant. This can only be done by comparing a 

 large series of perfect specimens, or by growing the different varieties 

 from the seeds of one. The plant has, however, some constant cha- 

 racters and a certain habit, the value of which is at once perceived and 

 admitted by the skilful botanist, though the uninitiated eye cannot 

 seize it. 



