Tukey • Horticulture is a Great Green Carpet that Covers the Earth 157 



now better known. No one today would 

 plant a solid block of Delicious apples, 

 Bartlett pears, Windsor sweet cherries, 

 or ]. H. Hale peaches. These varieties 

 have been found to be self-unfruitful 

 for one reason or another. The modem 

 orchardist must select varieties to in- 

 terplant for effective cross-pollination 

 and fertilization. And he would not use 

 as pollenizers such triploid varieties as 

 the Gravenstein and Baldwin apples, 

 nor the J. H. Hale peach, all of which 

 have defective pollen. This has been 

 the product of research. 



In commercial practice, the bee 

 may be used as the agent for pollinat- 

 ing with some regard to temperature, 

 bee flight, and number of bees required 

 for a given area. Traps have been de- 

 vised so that pollen is scraped from the 

 creatures as they enter the hive loaded 

 with pollen. In turn this pollen has 

 been placed in trays at the hive egress, 

 so that bees emerge coated with proper 

 pollen ready for business. Hand polli- 

 nation has been found practical in 

 some areas, and shot-gun shells loaded 

 with pollen have been fired with some 

 success at trees in the unfortunate 

 modem tempo of treating everybody 

 and everything as an adversary! 



Some plants, as the tomato and 

 cucumber will respond to applications 

 of certain chemicals such as para- 

 chlorophenoxyacetic acid for fruit set- 

 ting, and will produce seedless fruits 

 without pollination and fertilization. 

 Further, it has been found that the 

 tomato does not set fruit when night 

 temperatures are below 59° F. Under 

 such conditions, hand spraying with 

 plant regulating chemicals and raising 

 the night temperature by artificial cov- 

 ering, have both proved effective. 



Blossom thinning and fruit develop- 

 ment.— In recent years, securing a set 

 of fruit has become less a problem gen- 

 erally in orchard circles than thinning 

 off of excess fruits. Here it has been 

 found that early thinning is most effec- 



tive, beginning with blossom thinning. 

 Thinning of apples by means of blos- 

 som-thinning sprays has become stand- 

 ard practice in large areas, and there is 

 some success with peaches from ap- 

 plications several weeks after bloom. 

 Dinitrocresols have been used in some 

 regions, but growth regulators, such as 

 naphthalcncacetic acid and naphtha- 

 leneacetamide have been found more 

 effective in others. It has been learned 

 that such sprays tend to "knock off" 

 the weak blossoms and leave the strong, 

 so that the qualit}' of the remaining 

 fruit is improved both by reduction of 

 competition, and by "the survival of 

 the fittest." The concentration of the 

 chemical is adjusted to the variety', the 

 season, and the vigor of fruit buds. 



Studies with growth-regulating 

 chemicals have shown some possibil- 

 ities. For example, the Kadota and 

 Mission varieties of fig commonly set 

 fruit parthenocarpicallv, whereas the 

 Calimyma variety requires pollination 

 and fertilization. Yet this last named 

 variety can be caused to set fruit par- 

 thenocarpically by the use of certain 

 growth regulators and without the aid 

 of the caprifying wasp. It now appears 

 that the varieties which set fruit with- 

 out resort to pollination have a higher 

 content of native hormone than does 

 the Calimyma. Research shows that 

 fruit set and fruit development is re- 

 lated to liberation of specific hormones 

 by pollen, by endosperm, by embryo, 

 and probably by other parts. Extracts of 

 com pollen and of com embn'O will set 

 tomato fruits. It is not too much to 

 expect that the research worker will in 

 time appear with methods of control- 

 ling fruit set more exactly. 



Research in the field of plant regu- 

 lators has made, and is still making, 

 contributions to the horticultural in- 

 dustry equal to, if not greater than, 

 any other field of endeavor at the 

 moment. Not only are blossoms and 

 fruits both set and thinned, but the 



