8 



itself would not necessarily preserve the species unless 

 methods were adopted for a proper scattering of the new 

 individuals. 



It is sufficiently obvious that plants in general produce 

 a great number more offspring than has any chance of 

 arriving at maturity ; for instance, it has been calculated 

 that on an average a plant of the Shepherd's Purse" (Capsella 

 Bursa Pastoris), produces each season 64,000 seeds ; the 

 Henbane (Hyoscyamus Niger), 10,000. It has also been 

 reckoned that if every seed of henbane grew and produced 

 the average number, every one of which grew and produced, 

 that the entire area of the dry land of the earth's surface 

 would, in the short space of five years, be covered with 

 henbane plants. It can scarcely be to the advantage of 

 individual plants to produce seeds at the rate above indicated, 

 but the good of the individual is as nothing compared with 

 the good of the species, and rather than there should be any 

 risk of the stock dying out, seeds are produced at the 

 enormous rate above mentioned, proper means for their dis- 

 persal being provided, so that wherever there is an opportu- 

 nity of the plant successfully struggling against other 

 competitors in the race for life there shall be no lack of a 

 representative to make the attempt. 



There appears to be some law that the wider the area 

 of dispersal the greater the number of seeds or buds produced, 

 and vice versa, the smaller the area the less the number. 



This is strikingly exemplified when we consider the 

 difference between the number of seeds thrown off by plants, 

 and the number of new plants given off by means of runners, 

 suckers, tubers, or the like. The area of dispersal being 

 much greater in the former than in the latter. Take the 

 case of the Strawberry, the number of seeds produced on the 

 pericarp may in any one plant be many hundred, because the 

 chances of dispersal are considerable, on the same plant the 

 number of new plants produced by the runners will be only 

 ten or twenty, because the area of dispersal is strictly limited 

 to the inches over which the runners can travel. 



Of land plants I apprehend that the average distance 

 travelled by the seeds of any one species will be greatest in 

 those species in which the wind is the carrier, with perhaps 

 an exception I shall hereafter mention ; and accordingly we 



