MICHIGAN ACADEMY OF SCIENCE. 35 



SOME PHYSIOLOGICAL VARIATIONS OF PLANTS AND THEIR 



GENERAL SIGNIFICANCE. 



James B. Pollock. 



In a survey of the domain of the biological sciences in recent years, one of 

 the most significant facts is found in the extent to which physiology has in- 

 vaded those fields of this domain which, in the earlier stages of development 

 seemed entirely apart from and independent of physiological relations. 

 When species oi plants were supposed to have been created at the beginning 

 just as we find them today, and to transmit their original characters un- 

 changed to their remotest possible descendants, there was no physiological 

 cpestion as to the variations within species, and none as to the relation of 

 species to each other nor as to the origin of new species. In that view there 

 could be no origin of new species. They were all created at the beginning, 

 and then the Creator rested. 



When botany first began to be a science it was merely an attempt to clas- 

 sify plants, that is, to discover the characters of species as they were origin- 

 ally created, to group together those that were most alike and to separate 

 those that were unlike. The characters used in the first attempts at classi- 

 fication were more or less superficial, and systematic botany was merely a 

 study in formal external morphology. 



But a change has come; and this change began with the general acceptance, 

 among biologists, of the view that species are not entities with necessarily 

 fixed characters. Even though some species of plants have persisted with 

 constant characters ever since their earliest records were inscribed upon the 

 rocks, no biological theory has received more certain confirmation in recent 

 work than the theory that species are even now in process of creation. • The 

 creative power is not resting, never has rested. Species are appearing before 

 our eyes. We have only to open them and see. In short, nature has been 

 caught in the act of originating new species. 



I refer of course to the work of de Vries, who has found among the even- 

 ing primroses species which, every year, are giving rise to forms among their 

 offspring sufficiently different from, their immediate parents to be regarded 

 as elementary species. With some of these new forms the characters 

 w^hich distinguish them from their parents are constant when propagated 

 by seed. This is not to be regarded as the inheritance of characters acquired 

 by the parents of these new elementary species, but rather as the appearance 

 of new characters in the race, not by a gradual modification of parental 

 characters, but by a sudden transformation to which de Vries has given the 

 name mutation. These new characters cannot be ascribed to the direct in- 

 fluence of external factors on the adult or developing forms in which the new 

 characters appear, since they appear and persist in the same conditions of 

 life in which the parental type is continued. De Vries offers no explanation 

 as to how these new characters are produced, but following his Avork, Mac 

 Dougal has succeeded in producing new modifications by artificial means, 

 using as a subject of his experiments species which are closely related to 

 those wdth which de Vries obtained his notable results. Mac Dougal in- 



