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 on an average nearly 1800 
seeds. A small foxglove plant bears from 140 to 200 cap- 
sules and a large one from 5380 to 700. Therefore a single 
plant may produce over 1,250,000 seeds. A single orchid 
plant! 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 Mazxillaria, see Darwin’s Fertilization of Orchids, Chapter IX. 
