FLOWERING IN ITS BIOLOGICAL FRAMEWORK 3 



that the flowering process is essentially the same in all flowering 

 plants with only slight modifications which apparently lead to a 

 diversity of response. In my opinion it is too soon to draw this 

 conclusion. It has in the past led to application of findings obtained 

 with one plant to understanding of flowering in another — and 

 subsequent work has frequently failed to support this. 



We shall see in the next chapter that the diversity of response in 

 flowering is very great. If we want to make the classification scheme 

 complex enough, we can probably produce a separate category for 

 each species or variety. In many cases these differences are quite 

 striking. A short-day plant is inhibited in its flowering by a brief 

 light interruption of the dark period. A long-day plant is promoted 

 in its flowering by the identical treatment. In one short-day plant 

 far-red light is without eff'ect (or promotes) during the dark period ; 

 in another it inhibits flowering. The pendulum should be allowed to 

 swing far to the diversity side, and Chapter 2 is written to try to 

 push it far in that direction. 



But it must also be allowed to swing back to the uniformity side. 

 If there is any sort of natural relationship among the flowering plants, 

 as modern biochemistry implies, why shouldn't there be some basic, 

 common underlying mechanisms in the flowering process? There 

 are at least two excellent reasons to think that this is the case. The 

 pigment system which switches the plant's metabolism from the light 

 to the dark status seems to be common to all higher plants — 

 certainly to the ones which we will be discussing. Furthermore, there 

 is evidence from grafting experiments that the flowering hormone 

 itself is the same in species and varieties which in other respects show 

 opposite responses. 



Is the apparent diversity of response really only a matter of slight 

 modification of a common basic mechanism ? Or have the modifica- 

 tions become so extensive that we should not think in terms of a single 

 mechanism but rather of a number of fundamentally diff'erent 

 mechanisms which do happen to be similar in certain respects? 

 Much more research is required before these questions can be 

 answered, and so for the present we can only let the pendulum swing 

 freely while we wait for the facts to come in. The situation is, at any 

 rate, common to most of biology. We are impressed by the uniformity, 

 but the diversity is becoming more and more interesting. 



