48 THE NATURE-STUDY OF PLANTS 
iii. Those which produce them in flowers on 
separate plants. 
As a matter of fact, there are other and more 
complicated arrangements to be found, but there is no 
need to worry about them until the reader becomes 
an earnest student rather than a hobby-botanist. 
We will confine ourselves to these three types, and 
before we tackle the question how the pollen grains 
get to the stigma I must point out that if the pollen 
of a given flower reaches the stigma of the same 
flower it is called “ self-pollination”’; whereas if it 
reaches that of another flower, it is called ‘* cross- 
pollination.’? Of course the other flower may, or may 
not, be on the same plant, but in either event we will 
call it cross-pollination, and if we refer to the three 
types of flower to which I have just drawn attention 
we shall see that it is only the first that can be self- 
pollinated, the second may experience either sort 
of cross, but the stigmas of the third can receive 
pollen only from another plant. 
It is important to realize that it seems pretty 
certain that cross-pollination is in many ways better 
than self; it appears also that of the two possible 
kinds of crossing the benefit to the offspring is greater 
when the stigma receives grains from a separate plant, 
instead of from a different flower on the same plant. 
It would, however, be extremely difficult to prove 
either of these statements for ourselves, and we must 
be content to accept them on the great authority 
of Charles Darwin, to whose ability and indomitable 
patience every one of us owes a very great deal more 
than perhaps any of us realize. 
Despite the benefit of crossing we must, neverthe- 
less, remember that self-pollination is better than 
