THE PLUM IN KANSAS. 35 



recently shown the importance of cross-pollination with certain varie- 

 ties of pears ; and the same author says : "Apples are more inclined 

 to be sterile to their own pollen than pears. With the former, in the 

 great majority of cases, no fruit resulted from self-pollination." Beach 

 has shown that several varieties of grapes are more or less self-sterile, 

 and Green has added some useful notes in the same line. Bailey as- 

 serts that our native plums "do not fertilize themselves"; and the ex- 

 periments of Heideman with varieties of P. anierirana indicate not 

 only frequent self-sterility but also a remarkably capricious selective 

 affinity among certain varieties. It is in the A-B-C of strawberry 

 culture that certain varieties normally bear pistillate blossoms which 

 require pollination from other varieties, and that certain other sorts 

 are particularly useful for the quantity and prepotency of their pollen. 

 It seems possible, or even probable, that when we have gone a little 

 deeper into the question of the pollination of apples, pears, and plums, 

 we will designate their sexual capabilities and affinities as positively 

 as we do now those of the strawberry. It is evident that when our 

 knowledge of these fruits gains that degree of exactness we will have 

 made a great advance in pomology. In the meantime we may regard 

 it as the soundest practice to plant plum trees thickly together and to 

 to see that the varieties are well mixed. 



IV. CROSS-POLLINATION IN PLUMS. 



Cross-pollination is advantageous to many varieties of plums and 

 necessary to at least a few. This preference for foreign pollen is not 

 confined to the blossoms of cultivated varieties, but shows itself quite 

 unmistakably in many wild plums. The aboriginal forms of P. 

 americana seem to be especially delicate in their capabilities of 

 fecundation. To meet this need plums do not naturally depend alone 

 on the chance transfer of pollen by insects or wind, but cross-pollina- 

 tion is provided for and self-pollination is provided against by various, 

 interesting modifications of the typical flower. 



The form of the flower may be changed. There are possible six 

 distinct variations. In two of these the pollen and stigma mature at 

 different times ; in two forms the pistils are either much shorter or 

 much longer than the stamens ; and in two the flowers are sexually 

 imperfect, one or the other of the essential organs being defective. 



Any one of these arrangements in a blossom usually renders it in- 

 capable of self -fecundation. It is probable that each of these six 

 forms occasionally appears in plum blossoms, particularly in varieties 

 of the americana group, but aside from the one bearing imperfect 

 pistils, I am inclined to believe that these diversities have little im- 

 mediate significance. They may be of some slight interest to theo- 

 retical biology in throwing some light on questions of evolution, but 



