690 



SCIENCE. 



[N. S. Vol. XXIII. No. 592. 



conditions under which the coral has grown; 

 though it by no means follows that heredity plays 

 no part in determining the form of the growth 

 assumed by the corallum under any particular 

 conditions, and it may well be that the tendency 

 toward one type rather than another is inherited; 

 this, however, can only be established by experi- 

 ment. 



I have italicized the words: 'this, how- 

 ever, can only be established by experi- 

 ment. ' 



2. Are the intermediate specimens in the 

 intermediate area actually intermediate in 

 character or are they hybrids? 



The following known occurrence of hy- 

 bridization taken from de Vries suggests 

 that a similar phenomenon might occur in 

 the intermediate areas described by Dr. 

 Merriam. Bhododoidron intermedium is 

 an intermediate form between the hairy 

 and the rusty species from the Swiss Alps, 

 B. hirsutum and B. ferrugineum, the 

 former growing on chalky, and the other 

 on siliceous soils. Whenever these types 

 of soil occur in the same valley and these 

 two species approach one another, the hy- 

 brid B. intermedium, is produced, and is 

 often seen to be propagating itself abun- 

 dantly. As is indicated by the name, it 

 combines the essential characters of both 

 parents. 



De Vries says: 



It is not to be forgotten, however, that all 

 taxonomic distinctions, which have not been con- 

 firmed by physiological tests are only provisional, 

 a view acknowledged by the best systematists. 

 Of course the description of newly discovered 

 forms can not await the results of physiological 

 inquiries, but it is absolutely impossible to reach 

 definite conclusions on purely morphological evi- 

 dence. This is well illustrated by the numerous 

 discords of opinion of different authors on the 

 systematic worth of many forms. 



Until various physiological tests of the 

 kind referred to by de Vries have been 

 made, more than an hypothetical explana- 

 tion of the facts presented by Dr. Merriam 

 is impossible. 



I now wish to reiterate my opinion as to 

 the importance of the work of de Vries. 

 The great value of his work consists in 

 having shown that 'The origin of species 

 is an object of experimental investigation,' 

 and having furnished guidance not only as 

 to what experiments should be made, but 

 as to how they should be made. 



Davenport in his last report to the presi- 

 dent of the Carnegie Institution says: 



The factors of evolution are three — variation, 

 inheritance and adjustment. Studies may be 

 made on any one of these factors or all three 

 together; as a matter of fact, they can hardly be 

 studied wholly independently. 



The discussion to follow will cover in its 

 range each of these factors. 



As I have opened the discussion it might 

 be expected that I should furnish specific 

 data bearing upon these questions. I can 

 furnish instances that I have gleaned from 

 the writings of de Vries, Weismann and 

 others, and those recently published in 

 Science, but all of these rightfully belong 

 to others; I have, however, cited some of 

 them. Out of my own studies I can pro- 

 duce evidence in favor of the general the- 

 ory of evolution, I can present phylogenies 

 of genera and species that, I think, will 

 stand the test of rigid criticism, I can fur- 

 nish examples of the adaptation of struc- 

 tures, I can also show instances of varia- 

 tions in accordance with varying physical 

 conditions, but I do not know a single fact 

 relating to the Madreporaria that would 

 aid in forming a definite conclusion re- 

 garding the origin of variation or the 

 means by which adjustment is affected — 

 I repeat, 'or the means by which adjust- 

 ment is affected,' for the expression 'nat- 

 ural selection' is mostly used to raise a 

 cloud of mental dust behind which we 

 escape into our ignorance. 



I should like to say that the controlling 

 influences that govern the distribution of 

 corals are being studied as assiduously as 



