356 GROWTH FACTORS AND FLOWERING 



far-red-like effect. Another rLDP, Crepis leontodontoides, flowered 

 rather quickly when treated with GA, but also in this case the reaction 

 was not specific, judging by the number of leaves produced by treated 

 plants and those formed by old plants flowering in SD (!). Shoot 

 elongation is promoted by GA but not by far-red extension, at least 

 under the basic conditions of our experiments. Also Mimidus luteus, a 

 plant flowering both under red and f-rLD (long extension) appeared 

 to be in no way stimulated to flower formation by GA, even if the 

 shoot was very much lengthened under the treatment. Thus, in this 

 case, GA had, as in Centaiirea, a far-red-like effect on growth but 

 not on flowering even though flowering of Mimulus is also aUowed by 

 f-rLD. We must note, however, that Mimulus may easily escape 

 flowering also in natural conditions when cuhivated in deep shadow, 

 in which case vegetative bolting takes place. The action of GA must 

 be interpreted in connection with this fact. We shall add here that in 

 the annual Hyoscyamus the flower-promoting action of GA is a f-rLD- 

 like one, the flowering response of this plant being positive toward a 

 long far-red extension. 



If we now consider SDP, we find undoubtedly that they respond to 

 GA in a far-red-like way for shoot lengthening, but we cannot say 

 exactly the same of their flowering behavior (Lona, 1956b). In this 

 connection, in fact, we have never observed a real specific substitution 

 of GA for a far red flash in Xanthium cultivated on relatively LD, but, 

 conversely, we did find that GA action on SD individuals appears to 

 be very similar to that of a SD supplemented with a long far-red exten- 

 sion. 



From these observations, although they are limited, we may draw 

 the impression that a similarity between the effect of GA and that of 

 f-rLD (or far-red predominant action in the photoperiodic cycle) is 

 frequently exhibited by caulescent and also rosette plants in their 

 growth processes as intact plants. A few exceptions may be found in 

 rosette plants that also require some red supplementary light for 

 shoot elongation. In general, red light has the inverse effect of GA. As 

 far as flowering is concerned, the similarity of the two actions appears 

 even less general, but it still seems to be discernible in some of our 

 experimental tests. Frequently GA action does not correspond to that 

 of a rLD, especially when red light operates for a long time. 



