SY2 Bulletin 181. 



planted alone. They need the pollen of other varieties to make 

 them fruitful. Then we must do what some of our most intelligent 

 fruit-growers has been doing for years — plant other varieties near 

 them as pollinizers. Orchardists along the Atlantic coast liave been 

 obliged to do this with Kieffer. The Californians often iind it nec- 

 essary 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 established orchard practice. 



The History of the Self-Stekility 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 observe 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 pub- 

 lication of his work, in 1894: (Bui. 5, Div. Veg. Pathology), many 

 experimenters have continued the lines of study indicated by him. 



The unfruitfulness arising from self-sterility had been noticed 

 many years before by fruit-growers. The benefit which some vari- 

 eties gained by being planted near other varieties also had been 

 noticed, and mixed planting was often practiced with success, par- 

 ticularly with AVild Goose and Miner. There are now one hun- 

 dred and twenty-six entries in my bibliography of references to 

 " barren " trees in American literature before the appearance of 

 Waite's Bulletin in 1894. The real cause of this barrenness, how- 

 ever, was not known definitely before the experiments of Waite ; 

 although it had long been supposed l)y many to be the pollen. Of 

 late years many experimenters have done careful work along this 

 line. Among these are Goff, Waugh, Craig, Kerr, Crandall and 

 Heideman, on orchard fruits ; Beach, Earle, T. V. Munson. Whit- 

 ten and Green on grapes. The California and Oregon State Boards 

 of Horticulture are also making a special inquiry on the self-sterility 

 of prunes. 



