360 MANUAL OF TROPICAL AND SUBTROPICAL FRUITS 



" It was not until 1909 that attention was called to the true cause 

 of barrenness in D. kaki, and the year following the cause of sporadic 

 fruitfulness was learned. It was known years before to a few that 

 the flowers of D. kaki are of two kinds, pistillate and staminate, but 

 that this fact had any practical bearing on the problem of unfruit- 

 fulness did not seem to occur to anyone. More recently the existence 

 of perfect flowers, i.e., those containing both stamens and pistils, was 

 brought to light. These flowers have no practical bearing on the 

 problem, as they are rare, and from some cause or other not yet clearly 

 understood, their ovaries very seldom develop into mature fruit. 

 Since 1909, the results of more than twenty thousand hand pollina- 

 tions have fairly demonstrated that pollination will cause fruit to set 

 and grow to maturity, when without it no fruit would be produced. 



" The fruitfulness of certain trees or groups of trees in some seasons 

 and not in others, even when pistillate flowers were present in goodly 

 numbers each season, can now be explained by the fact that there 

 are certain horticultural varieties of D. kaki which produce staminate 

 flowers at irregular intervals. They may be found on certain trees 

 one season and not the next. Many seasons may elapse before they 

 appear again. It may even happen that never again are they pro- 

 duced, or they may be produced every other season. Many com- 

 binations of intervals or skips in the production of staminate flowers 

 are possible and probable. A number of them have been observed 

 and noted with references to particular trees. The staminate flowers, 

 when they occur on these trees, are abundantly supplied with pollen 

 and fertilize not only pistillate flowers on the same trees, but through 

 the agency of insects the flowers of many trees surrounding them." 



It was evident to Hume, therefore, that a variety was needed 

 which could be depended on for the production of pollen to 

 fertilize the flowers of trees which lacked the male element. 

 The search for such a variety brought several to light, and one 

 of them, the Gailey, is now recommended for planting as a 

 pollinizer. By setting one of these trees to seven or eight of 

 other kinds, productiveness is insured. Hume continues : 



" It must be emphasized that the behavior of D. kaki in its relation 

 to pollination, or of any other fruit for the matter of that, in any one 

 locality, is no index to its behavior under any other set of conditions. 

 Even though the conditions may appear to be the same, there are 

 differences which we are too dull to detect or too ignorant to under- 

 stand, but which nevertheless operate on the trees and influence the 

 results. It is a matter of observation that under certain local seasonal 



