148 PLANTS AND MAN 
be crossed again, a heterogeneous offspring is the 
result, displaying a variety of characters inherited 
from one or other original parent. The crossing of 
varieties, native or cultivated, has the same result. 
Hybrids occur in nature, but not very frequently. 
Insects visiting flowers are well known to confine 
their attention to a great extent to one species at a 
time, so as agents of hybridization they are not 
efficient. Again, many hybrids do not produce fertile 
seed, so that if they arise by natural means they are 
not perpetuated. In the garden, hybridizing has been 
resorted to largely; but its practice is not so ancient 
as the method of producing improved breeds by 
selection. 
The cultivation of specially selected forms is cer- 
tainly of remote origin, and probably goes back to the 
earliest days of agriculture: of early date, too, is the 
introduction into regions where they do not occur 
naturally of plants desirable for their use or beauty. 
The records of the cultivation of the Vine, for 
instance, go back for five or six thousand years in 
Egypt. Two thousand years ago Pliny writes that 
ninety-one principal forms could be reckoned in his 
day, though “the varieties are very nearly as number- 
less as the districts in which they grow.” Theo- 
phrastus, three hundred years earlier, discourses 
learnedly of the different kinds of cultivated Figs, etc., 
and their superiority over the wild kinds. These and 
other authors make frequent mention of plants intro- 
duced into Greece or Italy from the East for their 
usefulness or their pleasing qualities. Nowadays, the 
number of species cultivated, the innumerable forms 
of these which are grown, and the wide distribution 
