200 REPORT OF STATE BOARD OF HORTICULTURE. 



Finally, the stamens and pistils of a tree may not mature simultaneously, 

 which would make a tree unfruitful, unless pollen is supplied from other 

 sources. With many varieties of orchard fruits the pistil of each flower ma- 

 tures a little before the stamens : and not infrequently the stamens mature 

 before the pistil is ready to receive the pollen. But there is usually enough 

 variation in the opening of flowers on the same tree to promote pollination 

 with each other, and so prevent serious loss from this alternate ripening of 

 the sexes. Defective pistils, scanty pollen supply, and the premature ripen- 

 ing of either pistils or stamens may often be important in determining the 

 fruitfulness of a tree ; but the main cause of unfruitfulness in most self- 

 sterile varieties is the failure of the pollen to fertilize its associated pistils. 

 This cause cannot be removed, but its injurious results may often be pre- 

 vented by a judicious selection of varieties. 



A PRACTICAL APPLICATION. 



The practical bearing of the self-sterility problem is this : There are cer- 

 tain varieties of fruit which we wish to grow largely for the general market, 

 but we And that they are not productive when planted alone. They need the 

 pollen of other varieties to make them fruitful. Then we must do what some 

 of our most intelligent fruitgrowers have been doing for years — j^lant other 

 varieties near them as pollenizers. Orchardists along the Atlantic Coast 

 have been obliged to do this with Kieffer. The Calif ornians often find it 

 necessary with their prunes ; and many an unproductive orchard of Wild 

 Goose has been made fruitful by being partially top-worked with another 

 variety. Cross-pollination of varieties is no longer a theory : it is an estab- 

 lished orchard practice. 



THE HISTORY OF THE SELF-STERILITY DISCUSSION. 



There are at least sixty species of plants which are known to be often 

 sterile with their own pollen. The study of this problem had its origin 

 mainly in the investigations of Darwin. While Darwin was not the first to 

 ol)serve the value of cross-pollination, he so far exceeded his predecessors 

 in this, as in most other work, that the beginning of a systematic study of 

 self-sterility is usually dated from the publication of his "Origin of Species *' 

 in 1859. Self-sterility in orchard fruits was first studied by Waite, under the 

 direction of the United States Department of Agriculture. Since the publi- 

 cation of his work, in 1894. ( Bui. 5, Div. Veg. Pathology ) many experi- 

 menters have continued the lines of study indicated by him. 



The unfruitfulness arising from self-sterility had been noticed many years 

 before by fruitgrowers. The benefit which some varieties gained by being- 

 planted near other varieties also had been noticed, and mixed planting was 

 often practiced with success, particularly with Wild Goose and Miner. 

 There are now one hundred and twenty-six entries in my bibliography of ref- 

 erences to "barren" trees in American literature before the appearance 

 of Waite's bulletin in 1894. The real cause of this barrenness, however, was 

 not known definitely before the experiments of Waite : although it had long- 

 been supposed by many to be the pollen. Of late years, many experimenters 



