340 TRANSACTIONS OF SECTION K. 



3. Mutational v. Recapitulatory Characters. 

 By R. RuGGLES Gates, Ph.D. 



The cytological work on mutation has led to the view that each mutation is 

 the result of a nuclear change in a germ cell. In the last analysis this is either 

 a physical or a chemical change in the chromosomes. A chemical change in one 

 chromosome results in a new Mendelian character, which is handed down to 

 later generations just as the descendants of that chromosome are transmitted. 

 Mitotic cell division, by equally splitting all the chromosomes, ensures that the 

 change 'will be represented in every cell ; and so a mutation, in plants at least, 

 usually affects every stage of the ontogeny. Mitosis may thus be looked upon as 

 an hereditary process. 



In contrast to mutational or cell characters, which arise in the nuclei and 

 modify every stage of the ontogeny, we place recapitulatory characters, which 

 arise through the impress of the environment, usually involve adaptation to new 

 conditions, are gradually developed, and in becoming permanent involve the 

 principle of inheritance of acquired characters. 



These two classes of characters therefore differ in (a) their manner of origin, 

 (l>) their relation to organic structure, and (c) their relation to phenomena such 

 as recapitulation, adaptation, distribution, and inheritance. The theory of 

 antithetic alternation of generations, which is widely held as regards Archegoniate 

 plants, implies a gradual lengthening in the sporophyte through the addition of 

 cell divisions to its sub-terminal stages. This can hardly be supposed to have 

 resulted from an alteration in the cell unit. 



Characters which show recapitulation, as in the seedlings of Gymnosperms, 

 or the innumerable cases in animal larvae, imply a lengthening in the life cycle in 

 connection with a.daptation to new conditions. Such characters could not have 

 arisen through a mutation, for that would modify every stage instead of adding 

 certain stages as it does. The attempts of many zoologists to explain away the 

 remarkable facts of recapitulation have not been markedly successful. The 

 apparent contradictions of von Baer's law of animal development are partly due 

 to the occurrence of mutations in organisms which already show recapitulation. 



Thus both mutational and recapitulatory characters are necessary to account 

 for the phenomena of evolution. The one is nuclear in origin and centrifugal 

 in effect ; the other, extrinsic in origin and ultimately centripetal in its effect in 

 the organism. The recognition of both types of characters involves the limitation 

 of the cell theory and the admission <?f the neo-Lamarckian factor. 



4. The Fungal Species. By William B. Brieeley. 



In mycology the species group is at present conceived as ' all those individuals 

 possessing an essentially similar morphological fades.' This definition is based 

 on the following assumptions : — 



• 1. The essential specific characters of an organism are of a morphological 

 nature. 



2. The morphological characters are constant and hereditary. 



3. The essential morphological characters may be recognised and evaluated 



by sight in one specimen of one generation. 



It is, however, known that the Limiean species or ' Linneon ' in fungi may 

 consist of a group of elementary species or ' Jordanons,' and that each of the 

 latter may contain one or more true ' species ' or pure lines. It has also been 

 demonstrated that the morphological facies of a ' species ' is only constant under 

 constant conditions, and that development in a changed environment may give 

 rise to different morphological characters. The moi-phological facies of a fungus 

 is therefore merely the visible expression of the resultant of the interaction of 

 the physiological constitution of the organism, which ultimately is of physico- 

 chemical nature and of the physico-chemical factors of the environment. 



The true species concept is therefore physiological and not morphological, and 

 the species group is defined as ' all those individuals possessing an essentially 

 simVar •physiological constitution.' 



The physiological constitution of fungi may only be ascertained and compared 



