120 TROPICAL AGRICULTURE 



is borne on the male trees. Some male trees bear regularly 

 and quite heavily, but the fruit hang suspended on long pedi- 

 cles rather than being sessile on the side of the trunk as in 

 female trees. Occasionally, a female tree is found in which 

 the flowers are perfect. At the Hawaii Experiment Station 

 a flower on a tree of this type was self-fertilized and protected 

 from cross-pollination. The seed obtained from the resulting 

 fruit were all planted and as soon as the trees came into bearing 

 a selection was made of the most desirable type and on this tree 

 the flower was again cross-pollinated and a second generation 

 of trees obtained. This second generation included 454 trees 

 and a careful examination of these trees showed that 95 per 

 cent, were self-fertile. This gives reason to hope that within 

 a few more generations a self-fertile type will be established 

 which will obviate the necessity of cross-pollination and prevent 

 the endless variation which occurs from this method of 

 propagation. 



The papaya comes into bearing perhaps earlier than any 

 other fruit tree. Under favorable conditions large ripe fruit 

 may be obtained within n or 12 months from the time of 

 planting the seed. The trunk is succulent and starchy and 

 grows very rapidly. For commercial purposes it is perhaps 

 desirable to cut down the orchard and replant at the end of 

 3 years since the papaya tree has the peculiar habit of tapering 

 to a point, after which the fruit is extremely small. The 

 papaya is one of the few commercial plants in which it has 

 been found possible to change the sex by mutilation. At the 

 Hawaii Experiment Station, 22 perfectly sterile, staminate 

 papaya trees were beheaded. When the new growth appeared 

 on these trees it was found that two of the trees had become 

 strictly female trees bearing large fruit. Change of sex in 

 papaya has also been produced in one or two instances by other 

 investigators. 



The juice of the fruit, stem, and leaves of the papaya con- 

 tains an active ferment known as papain, a vegetable pepsin. 



