98 THE PLUM IN KANSAS. 



scarcely exceeds two hours, and is not, as many suppose, during the 

 whole life of the expanded flower. 



LEGITMATE AND ILLEGITIMATE FERTILIZATION. 



From the many artificial crosses that I have made and recorded, I 

 long ago became convinced that fertilization might be efiPected in dif- 

 ferent degrees, and that many plants had the power of throwing off" 

 such ovaries as were fertilized by pollen lacking in sexual affinity, and 

 that this was especially true in P. amerlcana. It should be borne in 

 mind that the production of seed is the chief end of the act of fertili- 

 zation, and the vivification of the ovule is the primary object of pol- 

 lination. By systematic crossing and hybridizing, I determined that 

 the union of the reproductive elements of two trees possessing the 

 proper selective affinity for each other readily produced a stronger de- 

 velopment of the ovary ; a union of this kind I shall call "legitimate." 

 It is well known that by crossing distinct species fertilization is effected 

 with more or less difficulty ; that reciprocal crosses of the same two 

 species vary in the intensity of fertilization. As to the union of the 

 reproductive elements of varieties lacking in sexual affinity for each 

 other, or in which the reproductive elements have become too greatly 

 differentiated and the development of the ovary either fails entirely or 

 is below the normal, I shall use the term "illegitimate," and in the 

 same sense as used by Mr. Darwin. 



The simplest test to determine the sexual affinity of any variety, 

 and one which I have never known to fail when under proper condi- 

 tions, is to take several sets of flower clusters and pollinate each indi- 

 vidual stigma with pollen of a different form. The union of such 

 crosses as posses the proper degree of affinity will prove fertile, while 

 the union of those lacking in affinity will j^rove sterile. No matter 

 how many of the flowers of each cluster are pollinated legitimately 

 or illegitimately, the result will be as above. If all of the flowers of 

 a cluster are pollinated legitimately, they will all set fruit, barring 

 accident, of course. This experiment may be modified by many dif- 

 ferent combinations. Of the forty-nine possible combinations, or 

 directions, of pollinations, but one form, the hermaphrodite, is fully 

 fertile with its own pollen. Including the hermaphrodite form, cross- 

 fertilization is legitimate in only thirteen directions. Thus, it will be 

 seen that, among the seven forms of P. amerlcana, jjollination is pos- 

 sible in forty-nine directions, thirty-six of them giving negative or 

 illegitimate results, and that there are only thirteen directions in 

 which cross-fertilization is possible. 



I know of no group of plants more favorable than the genus Prunus 

 for the study of the order of evolution from the hermaphrodite stage 

 to the higher stage of bisexuality. Their organs of reproduction, as 



