Cross and Self-Fertilization a3 
Cross and Self-Fertilization 
Working with cotton, the Arkansas Agricultural Experiment Station is testing 
the effects of cross and self-fertilization, in four different degrees, comparison being 
made of the results when blossoms are self-fertilized, when they are pollinated from 
other blossoms on the same plant, when pollinated from another plant of the same 
variety, and when pollinated from a plant of a different variety. Since Darwin’s 
classic experiments, very little notable work has been done in this field, but the 
claim of the harmlessness of self-fertilization, put forward largely on theoretical 
grounds by various recent students, renders it necessary that the question should 
be again taken up and new evidence procured. The Arkansas station hopes to be 
able, by this series of experiments, to get absolute measurements of the results 
produced by the various degrees of close-breeding. While the question is one of 
great theoretical interest, particularly for the bearing it has on the evolution of sex, 
it has also a practical importance; for if it were generally admitted that self- 
fertilization is injurious, breeders would change their methods in many cases. 
The question of cross- vs. self-fertilization and its effect on vigor should not be 
confused with the question of hybrid vigor, for there is little doubt that most 
first-generation hybrids show marked vigor—to such an extent that corn, tomatoes 
and many other crops are best grown from first-generation hybrid seed. The 
distinction which the Arkansas and other stations are developing, is rather along 
the line suggested by A. D. Shamel’s statement, in the second annual report of the 
American Breeders’ Association, that ‘‘Self-fertilized tobacco seed, the result of 
the closest possible degree of inbreeding, has been conclusively demonstrated by 
four seasons’ experience and experiments in extensive fields of different varieties of 
tobacco to produce more vigorous plants than seed cross-fertilized within the 
variety. Crosses of different strains of tobacco, however, give increased vigor of 
growth, leaf and seed production.”’ 
It should be noted that Darwin’s own experiments did not show self-fertilization 
to be detrimental in every instance. Notably in the case of the California poppy 
(Eschscholtzia californica), self-fertilized seeds produced plants which surpassed 
the plants from cross-fertilized seed, in three out of four cases. So it is possible that 
conditions may vary with different plants, although one is naturally inclined to 
suppose that a principle of such fundamental importance in the struggle for existence 
ought to hold good throughout nature. 
But even before this problem is finally settled, there are some lines in which 
breeders can work with great possibilities of commercial profit, and the Hawaiian 
experiment station has started one of these, by attempting to breed a strain of 
papayas (Carica papaya) with self-fertile flowers. The papaya, one of the impor- 
tant fruits of the tropics, is irregularly monoecious; obviously, if male trees could 
be altogether eliminated, a considerable saving would occur in planting. Since 
trees with perfect flowers are occasionally found, the station is endeavoring to 
make this type supplant the ordinary monoecious type altogether. The experiment 
is now in the second generation, in which more than 400 trees were raised; 96% 
of them were self-fertile, the few remaining trees not being exclusively male in 
character but showing a strong tendency to bear fruit. As in nature the males 
make up about half of the trees, the economy of space should be large when the 
new strain is perfected. 
