540 



SCIENCE. 



[N. S. Vol. XXI. No. 53G. 



found and sudden metamorphoses. In 

 these eases a particular activity, on which 

 must often depend the life of the indi- 

 vidual or of its progeny, has to be per- 

 formed with a high degree of proficiency 

 at its very phylogenetic inception or it can 

 be of no advantage to the individual or the 

 race. Such cases, with which you are all 

 sufficiently familiar, have ever been the in- 

 surmountable obstacle to the evolution of 

 instincts on the theory of fluctuating varia- 

 tions and natural selection. The theory of 

 organic selection seems to me merely to 

 conceal but not to overcome the difficulties. 

 The mutation theory frankly avoids the 

 difficulties even if it fails to throw any 

 light on the origin of the mutations, and 

 bundles this into the germ-plasma. It is, 

 of course, no objection to the theory that it 

 leaves something under the heavens to be 

 accounted for. This is rather to be re- 

 garded as one of its chief virtues. As 

 working naturalists we have reason to be 

 most suspicious of the theories that explain 

 everything. 



Discontinuous Variation and the Origin of 

 Species:* Dr. D. T. MacDougal. New 

 York Botanical Garden. 

 That distinct and separate qualities ex- 

 pressed in recognizable external characters 

 may appear suddenly, or disappear com- 

 pletely, in a series of generations of plants, 

 has been a matter of common observation 

 so long that it would be difficult to hunt 

 out and fix upon the first instance of 

 record. 



The significance of such phenomena was 

 obviously beyond the comprehension of the 

 earlier botanists, and it is evident that a 

 rational recognition of the phylogenetic 

 value of sports and anomalies necessarily 

 awaited the development and realization 



* See al.so, MafDoii^ial, ]). T., ' Discontinuous 

 Variation and the Oii^'in of Species.' Torreya. 

 5: .Jan., 1905. Pp. 1-6. 



of the conceptions of unit-characters, of 

 the minute structures which are the ulti- 

 mate bearers of heredity, and of the inter- 

 dependence of the two in such manner as 

 to constitute actual entities as embodied in 

 Darwin's pangenesis, de Vries' intra-cel- 

 lular pangenesis and in Mendel 's investiga- 

 tions upon heredity. It is equally ap- 

 parent that a proper interpretation of the 

 facts in question, and their distinction from 

 the results of hybridization were possible 

 only by means of the analysis of the col- 

 lated results of observations upon series of 

 securely guarded pedigree-cultures, in 

 which the derivation of all of the individ- 

 uals of several successive generations had 

 been noted. For it is now thoroughly real- 

 ized that the main questions of descent 

 and heredity and of evolution in general 

 are essentially physiological, and as such 

 their solution is to be sought in experiences 

 with living organisms and not by deduc- 

 tions from illusory 'prima facie' evidence, 

 which has been so much in vogue in evolu- 

 tionary polemics, nor by 'interpretations of 

 the face of nature' with the accompanying 

 inexact methods and superficial considera- 

 tions. It was upon the safe basis of the first- 

 named conceptions, and by means of the 

 methods entailed, that de Vries so success- 

 fully grappled with the problems involved 

 in the investigation of the part played by 

 discontinuous variation in evolution. 



In view of the amount of orderly and 

 well-authenticated evidence now at hand, 

 it may be regarded as demonstrated that 

 characters, and groups of characters, of 

 appreciable physiological value, originate, 

 appear in new combinations or become 

 latent, in hereditary series of organisms, in 

 such manner as to constitute distinct breaks 

 in descent. 



This is the main thesis of the mutation 

 theory— the saltatory movements of char- 

 acters, regardless of the taxonomic value of 

 the resultant forms. That the derivatives 



