244 SCIENCE PROGRESS. 



Returning to the second of the classes of cases se- 

 lected above — How far may we conclude that the peculiar 

 organisation of such specialised plants as Xerophytes, for 

 instance, are due to the continued action of their present 

 environment, and how far to the accumulated inherited 

 effects of the environment in the past? For that is what 

 the dispute between the two great schools amounts to. In 

 other words, how far will the plant continue to build up its 

 structures and assert its morphological individuality, inde- 

 pendently of variations in the environment, in virtue of the 

 machinery it possesses being compelled to work along 

 definite lines if the environment allow it to work at all ; 

 or how far can the action of the existing environment affect 

 the working of that machinery in the present, and bring 

 about variations which we can detect ? 



It is clear that experiment alone can give us information 

 here ; but the results of the experiments already made go 

 to show that we have still much to learn before we can even 

 realise the nature in detail of the problem to be attacked. 



Are we, when experimenting with a varied environment, 

 directing its actions on to a complex of structures which 

 are themselves the response to the continued action of this 

 environment ; or are other factors in play — e.o-, the ac- 

 cumulated and emphasised results of previous environments 

 handed down by heredity? 



Most botanists would probably say the latter, and in- 

 deed it seems difficult to see how the former could be 

 maintained, although some such assumption would appear 

 to lie at the foundation of some of the experimental en- 

 quiries started or proposed. 



It seems evident that a clear apprehension of this question 

 must precede any enquiry into the action of the environment 

 on plants, but that once obtained we need not be deterred 

 even by the enormous complexity of the subject from ad- 

 mitting that all the phenomena of morphology, including 

 the alternation of generations, are phenomena with physio- 

 logical questions behind them, and therefore subjects for 

 experimental enc|uiry. 



Glimpses are already to hand which show that such is 



