SEED DISPERSAL 253 



The feeling is not easily forced down that the 

 umbels overdo it. Then here is a healthy plant 

 of the humble chick weed. Some one has taken 

 the trouble to estimate its latent progeny, and has 

 concluded that if all its seeds grew up and their 

 progeny were in turn equally successful for just 

 three years, the family of the single original plant 

 would cover all the land space of the globe. Yet 

 chickweed is not much of a success, and would 

 be even less of a success than it is if gardening 

 and agriculture had never been invented. For, 

 though the gardener is its greatest enemy, it makes 

 but a poor show of it where he or the farmer 

 have not prepared the ground. 



With all their prodigality and all their clever 

 devices, the flowering plants are not by any means 

 such successful seed scatterers as the ferns which 

 in the modern world they have so nearly super- 

 seded. It is probably no exaggeration to say 

 that there are fern spores everywhere. Microscopic 

 in size, they fall in millions from the back of 

 every fertile fern frond, float in the air, and form 

 a part of the impalpable dust which just becomes 

 visible in an isolated sunbeam. In time they 

 reach the earth, and only wait the suitable con- 

 ditions to germinate. But the conditions suitable 

 to fern germination are relatively rare, and the 

 fern's plan for reaching them is to powder the 

 whole world. Thus if there are only half a dozen 

 spots in a country suitable for a particular fern, 

 that fern will be found in those places (or would 

 if collectors had never been permitted to wander 

 at large). From this it may be inferred that 



