THE STRUGGLE FOR EXISTENCE 391 



It is not difficult to see that the offspring of a single 

 morning-glory plant would, at this rate, soon actually 

 cover the entire surface of the earth. The fact that 

 morning-glories do not occupy any larger amount of ter- 

 ritory than they do must therefore depend upon the fact 

 that the immense majority of their seeds are not allowed 

 to grow into mature plants. 



There are many plants which would yield far more sur- 

 prising results in a calculation similar to that just given 

 than are afforded by the morning-glory. For instance, a 

 foxglove capsule contains 011 an average nearly 1800 

 seeds. A small foxglove plant bears from 140 to 200 cap- 

 sules and a large one from 530 to 700. Therefore a single 

 plant may produce over 1,250,000 seeds. A single orchid 

 plant 1 has been shown to produce over 10,000,000 seeds. 



459. Importance of Dispersal of Seeds. It is clear that 

 any means of securing the wide distribution of seeds is of 

 vital importance in continuing and increasing the numbers 

 of any kind of plant, since in this way destruction by over- 

 crowding and starvation will be lessened. 



A few of the means of transportation of seeds have been 

 described in Sects. 445-454, but the cases are so numerous 

 and varied that a special treatise might well be devoted to 

 this subject alone. 



460. Destruction of Plants by Unfavorable Climates. - 

 Land-plants, throughout the greater part of the earth's 

 surface, are killed in enormous numbers by excessive heat 

 and drought, by floods, or by frost. After a very dry 

 spring or summer the scantiness of the crops, before the 

 era of railroads which nowadays enable food to be brought 



1 Maxillaria, see Darwiu's Fertilization of Orchids, Chapter IX. 



