138 • A Miscellany 



enzyme or other substance is assayed in tissues at two quite different 

 stages of development; a difference is found, and this biochemical 

 difference is now suggested as the cause of the developmental 

 difference, in spite of the fact that it may be, and probably is, 

 merely a correlation. Such work may be quite interesting, bio- 

 chemically speaking, but the physiologist must always keep in mind 

 the need of a causal analysis. This at the very least requires atten- 

 tion to the kinetics— relations in time— of any two conditions, one 

 of which is believed to cause the other. The physiology of flowering 

 has had and will have its share of both sorts of biochemically 

 oriented investigations, but probably only the kind of care with 

 which Lang (1960) has started to analyze the relations between 

 endogenous gibberellin level and bolting in Hyoscyarnus will pro- 

 \ ide real understanding. 



Assuming, then, the goal of taking organisms apart bio- 

 (hemically-as long as the "parts" so obtained fit together again, 

 physiologically speaking— what other experimental approaches are 

 available? A useful one in the past will continue to be so: the 

 use of substances or conditions suspected of having relevant effects. 

 Though easily mocked, in some forms, as "spray and weigh," this 

 approach at least reduces the kinetics problem; the added substance 

 or changed condition surely precedes the effect in a well-controlled 

 experiment. However, the problem still remains of how directly 

 the two are related. It is this kind of approach, in the broadest 

 sense, that has led to the basic discoveries of photoperiodism and 

 vernalization, as well as many others. Even genetic studies come 

 into this general class. 



Advantages can be gained here from the use of more convenient 

 experimental materials. Arabidopsis, Chenopodium seedlings, and 

 Lemna are all small enough to be grown rapidly in aseptic culture 

 under highly controlled conditions, and may thus partially replace 

 the unwieldy Perilla and Xanthium of classical investigations. 

 However, the full exploitation of tissue culture techniques should 

 make the latter materials even more useful than ever for studies of 

 florigen and the induced state. For some preliminary thoughts and 

 results in this particular direction, see Chailakhyan (1961) and Fox 

 and Miller (1959). 



An approach related to the two preceding has not been 

 employed to any great extent. It involves following changes in 



