Remarks on the Nature and Definition of Species. 55 



logical analysis. Into this class fall, no doubt, many fungi, 

 since their secondary, dependent modes of nutrition render them 

 less capable of existence under a wide range of conditions than 

 the autotrophic plant. On the other hand there are many 

 plants even among the fungi, which seem to preserve their 

 identity closely over a wide selection of habitats. There is no 

 real difficulty involved ; these forms may indeed actually be in 

 the first category though responsive only to a limited range of 

 factors, common to all their habitats. Xo organism is sensitive 

 to every one of the almost infinite number of the complexities 

 of a natural habitat and many are extremely restricted, de- 

 pending only on the co-existence of a small number of widely 

 distributed influences and unaffected by a considerable latitude 

 in those to which they are not sensitive. The result from the 

 point of \'iew of practical s\'stematics is the same as before. 

 These types can be recognized as morphological entities with a 

 definite, though limited, physiological background. Whether they 

 are made up of a mixture of convergent races is another question, 

 which will only \ield to physiological, or let us rather call it, 

 ecological analysis; but we have already contested the assumption 

 that such races are themselves a whit less dependent upon 

 en\dronment for their apparent constancy than is the aggregate 

 form. 



To the conception of the organism as a physiological equi- 

 libration functioning about a constant point we must oppose 

 the modified conception of the organism in which nothing is 

 absolutely constant, but in wliich those morphological features 

 which have a relatively high quality of constancy deri\-ed from 

 extremely ancient habit, form the basis upon which the specific 

 character is superposed by the enWronment. 



Such a resurgence of Lamarckianism into evolutionary 

 thought will not surprise those who are acquainted with the 

 work of Perrier and Gra\ier on Tachygenesis* and the exposi- 

 tion on "Mutations and Evolution" by Gates-'-; but those who 

 wish to see how the importance of somatogenic characters has 

 impressed itself on a mutationist should turn to the latter series 

 of papers!. 



Brierley, in the paper already mentioned, draws a contrast 

 between the dynamic and static ideas of the species, into which 

 it would be idle to enter critically without essaying an analysis 

 of the meaning to be assigned to the term "existence." Suffice 

 it to say that if we accept the concept of organic form outHned 



* Perrier, E. and Gra\ner, C. L., La Tachygendse. Ann. Sci. Nat. Zool. xvi, 

 p. 133 (1902). 



t Gates, R. R., Mutations and Evolution. New Phj-iologist, xix, p. 26 

 (1920). J Now reprinted in book form. 



