158 



HORTICULTURE 



time of blossoming may be delayed. 

 Maleic Indrazidc has proved suited to 

 the raspbcrn' and related brambles. No 

 practicable method of delaying frnit 

 blossoming of tree fruits has jet been 

 devised, but the possibilities are there. 



Sprays of certain plant regulators, 

 as indolebut\ric acid, applied to de- 

 veloping figs at the proper time cause 

 them to ripen 14 davs after treatment 

 as compared with 75 days for typical 

 development of non-treated fruit. The 

 stravvberr)' fruit develops because of the 

 diffusion of plant regulating materials 

 from the achcnes which dot its surface. 

 About the sixteenth day after bloom, 

 the supply of regulator is low. Addi- 

 tional amounts of synthetic regulators, 

 as beta phenoxyacetic acid, applied at 

 about this time apparently induce con- 

 tinued growth and increased size. Im- 

 proved size of blackberries has similarly 

 been secured by similar treatments. 



Tlie application of plant regulators 

 to prevent pre-harvest drop of fruit has 

 become standard practice with both ap- 

 ples and pears. The action is apparently 

 to delay the development of the abscis- 

 sion zone in the pedicel of the fruit. 

 Napthaleneacetic acid and naphtha- 

 leneacetamide are the materials most 

 frequently employed. Proper timing 

 with relation to temperature, rainfall, 

 and fruit development is critical. 



Blossom induction and .photo- 

 period.— One of the features of Horti- 

 culture is that it frequently removes 

 plants from their natural habitat and 

 places them in an environment where 

 one or more climatic variables is 

 markedly altered. 



Light, daylength, temperature, nu- 

 trition, and various chemicals treat- 

 ments have been shown to induce 

 blossom formation. Thus in the case 

 of the tomato, a cool temperature early 

 in the life of the plant induces the for- 

 mation of flower clusters, a fact which 

 explains why northern tomato plants 



grown in the field directly from seed 

 may in a cool season produce fruit 

 earlier than from southern-grown trans- 

 planted plants. 



An undesirable effect of early cool 

 temperatures is found with early celery. 

 When exposed to cool temperatures, 

 blossom formation is induced and seed- 

 stalks are produced (bolting) which 

 makes such celery unsaleable. Lettuce 

 tends to form blossoms and seedstalks 

 with high summer temperatures and 

 long days. Breeding programs for these 

 crops are aimed at selecting plants with 

 "non-bolting" characters. 



Some plants, as the chrysanthe- 

 mum, respond to short daylength. By 

 extending the daylength with artificial 

 light, plants may be prevented from 

 forming flowers. By reducing day- 

 length, they may be induced to flower. 

 By proper attention, chrysanthemums 

 can be brought into flower at any 

 month of the year. 



Other plants, as the cineraria re- 

 spond to long daylength and may be 

 similarly controlled in flower formation 

 by adjusting the daylength. 



More recently, the gibberellins have 

 been shown to affect flowering in sev- 

 eral plants. Applications of gibberellie 

 acid to some biennial plants, as the 

 carrot and the collard have resulted in 

 these plants developing as annuals. 



Environmental adaptation of horti- 

 cultural plants.— It is known that cer- 

 tain areas are suited to peaches, others 

 to pears, potatoes, celery, and so on. 

 Yet too much of this has been learned 

 by bitter experience. The new tech- 

 nique is to study adaptation by eon- 

 trolled experiments and to be able to 

 predict. Thus, branches of trees are 

 enclosed in cooled and in heated 

 chambers as desired to simulate differ- 

 ent climatic conditions. 



Delayed dormancy of fruit trees is 

 another problem in adaptation which 

 has been met by research. Considerable 



