372 PLANT GROWTH SUBSTANCES 



and the well-known defects of puffiness, green pulp in the seed locules, 

 and premature softening. The use of whole plant sprays as compared 

 with flowei cluster sprays has at times reduced the set of fruit probably 

 because of the inhibiting effects of growth substances upon the young 

 flower buds (31,34). The application of growth substances to the soil (37) 

 has been eff'ective in setting tomato fruit, but such a technique suffers 

 from the same disadvantages as whole plant sprays in adversely affecting 

 the development of young flower buds. 



On outdoor tomatoes when hormone chemicals are applied to the 

 flower clusters early in the season, while night temperatures are still 

 below 55°F., the normal reproductive processes of pollination and fer- 

 tilization are totally nonfunctional. The growth substances provide a 

 complete replacement rather than a supplement. Results as measured 

 by early yield and size increases have been more phenomenal than any 

 reported for greenhouse tomatoes. In the field excellent fruit set and 

 quality is obtained, and the fruit is completely seedless. A change of 

 weather to warmer nights, in turn, will result in normally seeded fruit, 

 and httle or no response to hormone treatment except in fruit size. 



The use of whole plant sprays or dusts is desirable if growth substances 

 are to be utilized for improving fruit set and yields on large commercial 

 outdoor plantings. Success in their use on greenhouse crops has been 

 reported if one avoids spraying the growing tips (33), an impractical 

 precaution with field power equipment. Considerable work is in progress 

 on the use of whole plant apphcations for canning tomatoes (57). 

 Increases in early and total production have been obtained, but these 

 are not always equal to those reaHzed when the chemical is confined to 

 the flower clusters. As a flower cluster spray, the most effective chemical 

 has consistently been CIPA at a dilution of 30 ppm. Considerable evi- 

 dence supporting this has been accumulated not only in Michigan 

 but elsewhere (27,29). Alpha-ortho-chlorophenoxypropionic acid (ClPP) 

 at 75 ppm. has also been relatively effective as a flower cluster spray and 

 gives no leaf distortions or formative effects. When ClPP is used at 

 20 to 40 ppm. as a whole plant spray good results have been obtained, 

 but an immediate response in fruit setting comparable to flower cluster 

 spraying is not realized. 



The incidence of blossom-end rot associated with hormone treatment 

 of tomatoes has attracted the attention of physiologists since water 

 relations of the plant are involved, which, in turn, may be influenced 



