- 4. - 
is absolutely essential to the best fruit-formation. This is particu- 
larly true of certain varieties of the pear. A poor quality of fruit 
can be prevented only by growing together different varieties. Again, 
although a plant may readily pollinate itself, yet the pollen from 
another plant or variety may be prepotent over its own. This is to 
say, if the plant be pollinated by its own pollen along with that of 
a foreign variety, that of the foreign variety will usually effect 
fertilization . 
pp. 2734-5: The flowers of insect-pollinated plants, on the 
other hand, are usually showy, and have nectar or fragrance, or both. 
The pollen is more or less moist or sticky, so that it is not easily 
blown away... As the insect reaches down for the nectar, which is near 
the bottom of the flower, some parts of its body are sure to become 
dusted with pollen... Thus cross-pollination, or the transfer of pollen 
from the anthers of one flower to the pistil of another, is accomplished. 
[Bees collecting pollen are Just as valuable as those gathering nectar. 
In visiting large flowers they may be more effective, as they go directly 
to the reproductive organs.] 
The value of crossing to plants was first clearly proved by 
Charles Darwin in 1859... From the observations of Kolreuter, Sprengel, 
Knight, and his own exhaustive experiments, Darwin showed that co n- 
tinued self-fertilization is likely to result in Inferior offspring ; 
while cross-fertilization, within certain limits, gives greater vigor 
to the offspring. Cross-fertilization between different flowers on 
the same plant usually has no appreciable advantage. 
p. 2736: In the selection of a pollinizer, several points 
must be considered: (1) The two sorts must blossom approximately at 
the same time in order that cross-pollination may be possible. The 
transfer of pollen from one variety to another is performed mainly by 
insects. Waugh and Backhouse have shown that practically none of the 
pollen of the plum and other stone-fruits is carried by wind, it being 
moist and sticky. The same is true of pears, but apple pollen is 
somewhat drier and is wind-blown to a slight extent. The honeybee is 
the most important pollen-carrier. Hooper estimates that in England 
30 per cent of the cross-pollinaticr. is done by the hive bee. 15 per 
cent by various wild bees, especially the bumble-bee, and 5 per cent 
by miscellaneous insects . 
llf this was true for England with its large areas devoted to hedge- 
rows, woods, and small-scale farming with many wild areas suitable for 
the nesting of native bees, then in this country with its large blocks of 
clean cultivation, dwindling wild areas, its large sheep population and 
much greater use of arsenicals, the percentage of pollination effected by 
the honeybee must be even higher.] 
