122 THE WORLD OF LIFE 



but one of many hundred or even thousandfold annually. A 

 full-grown oak or beech tree is often laden with fruit on every 

 branch, which must often reach 100,000, and sometimes per- 

 haps a million in number, each acorn or nut being capable, 

 under favourable conditions, of growing into a tree like its 

 parent. Our wild cherries, hawthorns, and many other trees, 

 are almost equally abundant fruit-bearers, but in all these cases 

 it is only rarely (in a state of nature) that any one seed grows 

 to a fruit-bearing size, because, all having a superabundance 

 of reproductive power, an equilibrium has been reached every- 

 where, and it is only when some vacancy occurs, as when a 

 tempest uproots or destroys a number of trees, or some diminu- 

 tion of grazing animals allows more seedlings than usual to 

 grow up, that any of the seeds of the various trees around 

 have a chance of sun'iving; and the most vigorous of these 

 wall fill up the various gaps that have been produced. 



But it is among the herbaceous plants that perhaps even 

 gi'eater powers of increase exist. Where our common fox-glove 

 luxuriates we often see its tall spikes densely packed with 

 capsules, each crowded with hundreds of minute seeds, which 

 are scattered by the wind over the surrounding fields, but only 

 a few which are carried to especially favourable spots serve 

 to keep up the supply of plants. Kerncr, in his Xatural His- 

 tory of Plants, tells us that a crucifer, Sisymhrium Sophia, 

 has been found to produce on an average 730,000 seeds, so that 

 if vacant spaces of suitable land existed around it, one plant 

 might, in three years only, cover an area equal to 2000 times 

 that of the land-surface of the globe. A close ally of this, 

 Sisymhrium Irio, is said to have sprung up abundantly among 

 the ruins of London after the great fire of 1666. Yet it is 

 not a common plant, and is a doubtful native, only occurring 

 occasionallv in En2^1ish localities. 



Turning to the animal kingdom, we still find the repro- 

 ductive powers always large and often enonnous. The slowest 

 breeding of all is the elephant, which is supposed to rear one 

 young one every 10 years ; but, as it lives to more than 100 



