A. E. MURNEEK 33^ 



van Overbeek (70,71) reported that flowering in the pineapple, a rather 

 abnormal parthenocarpic fruit, can be induced with certain synthetic 

 growth regulators. About 50 milliliters of naphthaleneacetic acid (NAA) 

 or 2,4-dichlorophenoxyacetic acid (2,4-D), at a concentration of 5 parts 

 per million, when applied in the whorl of leaves near the apical meristems, 

 resulted in practically all instances in the formation of floral primordia. 

 Too high a concentration of NAA, however, retarded the time of 

 flowering as long as 4 to 8 months (15). Through further tests by van 

 Overbeek this treatment has been put to large scale commercial use. 

 Till a few years ago this was the only instance where flower initiation was 

 controlled by a growth regulator. The following currently published 

 information has further bearing on this point. 



By spraying leaves of Xanthium plants with indoleacetic acid (lAA) 

 and NAA solutions Bonner and Thurlow (6) were able to suppress 

 initiation of floral primordia during the induction (short-day) period. 

 The same results were secured when only 2 leaves of this plant were 

 submerged nightly during the dark period in a NAA solution of a 

 concentration as low as i mg. per Hter. In this experiment (6) and a 

 parallel one (7), 2,4-dichloranisole, an antagonist of auxin, counteracted 

 the inhibition of the above chemicals on formation of flowers. Moreover 

 when 2,4-dichloranisole or triiodobenzoic acid were apphed to leaves 

 of long-day vegetative plants, flowerlike buds were produced. Leopold 

 and Thimann (46) were able to increase by as much as 35 per cent the 

 number of flowers in barley by applying a weak solution of NAA through 

 the cut surface of leaves. It is of interest to note that relatively high 

 concentrations of the same substance inhibited flower formation. Since 

 both flowering and growth were promoted by relatively low concentra- 

 tions of NAA, the authors conclude that "these evidences indicate that 

 the growth hormone, auxin, is not necessarily opposed to the functioning 

 of the proposed flowering hormone, but rather influences it in a manner 

 qualitatively similar to its influence on growth." 



It would seem desirable to know whether NAA in this instance, while 

 stimulating growth in general, did not retard the multiplication of apical 

 cells in the vegetative meristems thus leading to the formation of 

 reproductive tissues. It has been shown that many synthetic growth 

 regulators may delay or inhibit cell division in the meristem (3,5). 

 In investigations of this kind cytological and chemical studies of terminal 

 meristematic regions during the earliest stages of induction would seem 



