GENERAL DISCUSSION OF RESULTS. 131 



Purely as a working hypothesis, to be tested and limited by further 

 investigation, the law of diminishing variability may be stated in the 

 most general foi-m to cover the facts in different fields, as follows: In 

 a continuous series of biological phenomena in which the same or homol- 

 ogous processes are repeated, the variation exhibited in the results of these 

 processes diminishes with successive repetitions. 



In the opinion of the writer any attempt to develop a detailed theo- 

 retical explanation of why the two laws of growth which we have found 

 in Ceratophyllum come to operate, would at present be premature. 

 Just now there is a much greater need for quantitatively definite facts 

 than for theories in the field of morphogenesis. What is, however, of 

 great importance on the theoretical side is to see exactly the nature of 

 the fundamental problem on which the interpretation of these growth 

 laws depends. We have seen that there is a definite functional relation 

 between the morphogenetic activity of a growing bud at any given time 

 and its previous activity or "experience. " In what way this functional 

 relation is brought about is the fundamental problem which lies before 

 us if we are to interpret our laws of growth. It will probably have oc- 

 curred already to the reader that our results are a very clear cut exam- 

 ple of the general principles which Semon ( :04) has recently developed 

 at great length. The influence of earlier upon later whorl production 

 might very well be described as the result of "engrammatic" action on 

 the bud in the formation of first and succeeding whorls. In fact, the 

 whole of our results seem to form a most striking and complete illus- 

 tration of the working out of Semon 's principles in a particular case 

 of ontogeny. But one can not escape the feeling that to attempt to 

 interpret the facts in this way is simply to redescribe them in a new 

 terminology without any substantial gain. Semon's rather obvious 

 argument to meet such a criticism, which he of course foresees, that all 

 science is only description, does not adequately remove the difficulty. 

 What we require in cases like that with which we are here dealing is a 

 description in terms of known physiological principles, and this the 

 "mnemnic" terminology does not seem to provide. It seems to the 

 writer that a more promising hypothesis on the basis of which to inter- 

 pret such morphogenetic phenomena as those which have been set forth 

 for Ceratophyllum might be developed along the lines suggested 

 in recent papers by Holmes ( :04) and Schieff erdecker ( :04) . Such an 

 interpretation has been worked out by the writer for use as a working 

 hypothesis in further investigations in this field which are now in 

 progress, but until it has been tested it hardly seems worth while to 

 publish it. 



