806 D. P. Gowing 



1-naphthaIeneacetic acid (NAA) for flower induction in this plant re- 

 sulted in a suppression of slips.- However, p-chlorophenoxyacetic acid 

 (PCA) induces slip production in plants forced with NAA. These two 

 materials, although both auxins in growth responses and although 

 both will induce flowering in the pineapple, are actually antagonistic 

 in this other morphogenic response. When the two are applied at vari- 

 ous rates in combination, the NAA offsets the slip-producing activity 

 of PCA. Other instances of antagonism in morphogenic effects have 

 been reported by the writer, e.g., that of indole-3-acetic acid for NAA, 

 and of indole-3-acetic acid for indole-3-butyric acid in the flowering- 

 induction response in the pineapple (2, 3). The horticulturist seek- 

 ing a chemical to give a morphogenic response cannot afford to as- 

 sume that if one growth regulator is active, the activity of all others 

 will be in the same direction, and only to a greater or lesser extent. 



A further point which has been but little investigated is the range 

 of morphogenic responses assignable to various levels of application, 

 short of outright toxicity. As an example of the importance of the 

 proper level of growth regulators to obtain a particular response, the 

 inhibition of flowering in pineapple by NAA may be mentioned. A 

 number of years ago, Clark and Kerns (1) reported that NAA at a 

 concentration of 10 p. p.m. induces flowering, but suppresses flowering 

 at 1,000 p. p.m. 



The induction of flowering by NAA has been a regular practice 

 for a number of years, but the chemical inhibition of flowering on 



Sep Dec Mar Jun Sep Dec Mar Jun Sep Dec Mor Jun Sep 

 I I I I 1 I I I I I I 



Planting Fruit Init. Harvest 



Vegetative Growtti I Fruit Devel. 



I I 



Planting 



Normal Fall Slip Planting 



F.I. I"!- *"•,'• H. H. H. 



Foil Sucker Planting 

 Planting 



Fl. Fl. Fl. H.FIH.FI. H. Fl. H. H. H. 

 >- 1 1 1 I I I I I I I I I 



Off-season Slip Planting 



Fig. 2. A sketch of the circumstances of pineapple crop production under Hawaiian 

 conditions. Year-around harvest (H.) is desirable for cannery operations. However, 

 several periods of fruit initiation (F. I.) in a given field are costly. (See text.) 



'The slip is morphologically a fruit, but is overwhelmingly vegetative rather 

 than fniitlike in its development and is tlie preferred planting material for succeed- 

 ing crops. It is borne on tlie peduncle just as is the fruit, in distinction to the 

 crown, a vegetative organ borne on the top of the fruit, and the sucker, which is a 

 branch off the main stem. Slips and suckers normaiiv develop at the time of natural 

 fruit initiation, and ihc crown is initiated after the florets of the inflorescence have 

 been laid down. 



