224 THE STORY OP THE PLANTS. 



and such mongrel forms often show us every 

 possible variation between the two parents. 

 But this can only happen when the parent stocks 

 are very close to one another; and even then, 

 the hybrids tend to die out rapidly. Why? 

 Because each of the parents is better adapted to 

 a particular situation ; the hybrid usually falls 

 between two stools, and gets killed down accord- 

 ingly. It cannot stand the competition of the 

 true species. New kinds, however, may some- 

 times take their rise from chance hybrids,, 

 which happen to possess some combination of 

 advantages. 



Thus plants in the mass, as we see them 

 around us at the present day, are divisible into 

 several well-marked groups, some of which are 

 now dominant or leading orders, while others 

 are hardly more than mere belated stragglers or 

 loitering representatives of types once common, 

 but now outstripped in the race by younger 

 competitors. I cannot close without briefly 

 describing to you the main divisions of such 

 orders or groups, as now accepted by modern 

 botanists. 



The widest distinction of all between plants is 

 that which marks off the simpler and earlier 

 forms, which are wholly composed of cells, from 

 the higher and stem-forming types, which are 

 also provided with systems of vessels and woody 

 tissue. The first class is known as CELLULAB 

 I PLANTS ; the second class as VASCULAR PLANTS. 

 These are the greatest and most general 

 divisions. 



