22 INTRODUCTION 
which the pollengets from theanther to thestigma 
is called pollination. In case the pollen comes. 
from the same flower it is said to be a case of 
self-pollination; in case it comes from another 
flower, perhaps upon the same plant but preferably 
upon another plant of the same species, it is said 
to be a case of cross-pollination. In general we 
know that flowers exist chiefly in order that they 
may attract insects to bring about cross-pollina- 
tion and the consequent cross-fertilization that 
results. As Darwin said, “nature abhors per- 
petual self-fertilization.” 
Cross-pollination may take place through the 
agency of winds, of birds like the humming-bird, 
and of insects. The great majority of our com- 
mon flowers have the pollen carried by insects. 
Such flowers are said to be entomophilous or 
insect-loving flowers, while those which depend 
upon the wind for the carrying of their pollen are 
said to be anemophilous or wind-loving flowers. 
It not infrequently happens that the nectar in 
the flower is protected from the visits of ants and 
other wingless insects, which would not make 
effective pollen carriers, by some such special 
device as a fringe of hairs within the corolla or 
sets of viscid hairs upon the outside of the flower. 
From the point of view of the life relations of 
the plant three questions may be asked in regard 
to any flower, namely: 
