Introduction. 9 
certain appendages and coverings, which in function may 
be quite indistinguishable from others belonging to the 
fruit. A seed, therefore, for our present purposes is the 
one-seeded unit of dispersal. All our British fruits, with 
the single exception of that of the Cornel, divide into such 
one-seeded portions, which tend to be dispersed separately, 
so that the young plants do not interfere with each other. 
These units may be seeds in the strict botanical sense, or 
they may be complete one-seeded fruits ; sometimes they 
are stones or carpels, one-seeded, or at any rate with only 
one of the seeds properly developed; in other cases they 
include the dried calyx, or other parts of the flower or 
receptacle. Constant explanation would be needed if an 
attempt were made to define botanically what part of the— 
fruit is referred to in each case—it is more convenient to 
accept the perfectly understood popular usage. 
