10 



THE POLLINATION OP PEAR FLOWERS. 



crossing- to plants, and lias collected in snx)port of liis views many ob- 

 servations of others. The principles stated in the above book were the 

 main incentives and guides to the experiments recorded in this bulletin. 



In his Variation of Animals and Plants under Domestication, Darwin 

 brought out new and additional evidence bearing on this subject. The 

 important laws which his investigations have so clearly demonstrated 

 are now universally accepted by naturalists. They may be briefly 

 stated as follows : (1) Nature abhors perpetual self-fertilization ; (2) con- 

 tinued self-fertilization is injurious, resulting in inferior and less fertile 

 ott'spring; (3) cross -fertilization is necessary for the production of 

 healthy seedlings; (4) jjlants are endlessly modified to secure this end. 

 The whole matter is interwoven with another great law of Darwin's, 

 the law of natural selection, in which he shows how cross-fertilized 

 individuals, being naturally strong and vigorous, crowd out and survive 

 the competition of both their own and other species and propagate their 

 kind. 



Hermann Miiller, in his important work on the Fertilization of Flow- 

 ers, in which he includes a vast number of observations on the methods 

 by which plants are pollinated, points out not only the modifications 

 Avhich flowers undergo for the purpose of cross-pollination, but also 

 the corresponding changes in insects, which enable them to secure 

 nectar and pollen from the flowers and at the same time cross-pollinate 

 them. This correlation of flowers and insects is admirably discussed 

 in a little volume by Sir John Lubbock, entitled British Wild Flowers 

 ill their Relation to Insects. Since the publication of Darwin's Origin 

 of Species many investigators have studied this attractive subject, and 

 the result is a vast store of literature. A nearly complete list of the 

 works on the subject up to 1886 is to be found in Miiller's book above 

 mentioned. 



While many plants have contrivances for securing cross-pollination 

 by insects, there are many others that are pollinated by the wind, nota- 

 l)ly, for examx)le, the pines, the cereals and other grasses, and the sedges. 

 Such plants always have inconspicuous flowers without showy corol- 

 las. They produce large quantities of dry and dust-like pollen, which is 

 easily carried long distances by the wind, and their pistils are generally 

 long and feathery, so as to catch the flying pollen. It will be shown 

 later on that the pear flower from its very structure does not fall in 

 this category. 



Botanists look upon most flowers which are modified so as to have 

 showy corollas and attractions in the way of nectar and perfume as 

 developed for insects and by them through the agency of natural selec- 

 tion. The real purpose of the numerous modifications Darwin has dem- 

 onstrated is to secure cross-fertilization.* Thus the reader will readily 



* Those who wish to read further on this important subject are referred to the 

 above-mentioned works of Darwin, Miiller^ and Lnbbock. An extellent work in 

 German, Pflanzenleben, by Kerner von Mirlaun, should also be mentioned, since it 

 contains much interesting information in this line. 



