146 Varietäten, etc. — Palaeontologie. 



rited (germinal) form of fasciation, uninherited (somatic) form of 

 fasciation. Review of Mendelian studies {Pisum, Zea). Special study 

 of fasciation in Nicotiana. General discussion, showing the bearing 

 of these data on certain general problems of heredity and evolu- 

 tion. The character fasciation is widely distributed in the plant 

 world, both in wild and cultivated plants. Sufficient data haye not 

 been collected to prove that it is absent from any taxonomic group. 

 Certain ecological conditions are favorable to its development, but 

 these conditions are not necessarily essential. The character fascia- 

 tion may occur in almost any part of the plant. Morphologically, it 

 appears to be an enlargement of a Single growing point, so that 

 considering the fasciated plant as a whole, the amount of tissue is 

 greatly increased over that of its normal relatives. Very numerous, 

 diverse internal and external factors operate singly or in combina- 

 tion to develop fasciation. If these factors are largely internal, and 

 the race is naturally cleistogamous, the character is generally here- 

 ditary and constant. If the factors are largely external (insect de- 

 predation, mutilation etc.) the character fasciation is neither here- 

 ditary nor constant. If the fasciated race, to begin with, is not 

 genotypically homozygous, as is not the case when the individuals 

 of a species are naturally cross-fertilized, the character fasciation 

 may be hereditary, but present in only part of the progeny, owing 

 to the segregation of the primary internal factors for fasciation or 

 to the segregation of numerous other internal factors which may 

 modify in some manner the expression of those factors especially 

 concerned in the production of fasciation. From the Standpoint of 

 genetics all fasciations may be divided into two classes: Inherited 

 and uninherited, the former due primarily to one or more genetic 

 factors, the latter largely the result of environmental conditions. 

 The „half" and „eversporting" fasciated races of de Vries probably 

 belong largely to the latter class. No necessity exists for and con- 

 fusion results from maintaining the conception of „eversporting" 

 fasciated races. Had the studies of de Vries been made at the 

 present time rather than in the pioneer period of genetics, it is 

 safe to say that this conception would never have arisen. Domi- 

 nance and recessiveness in the case of the character fasciation is 

 always dependent on the 3 elements held to be the basis of a cha- 

 racter: the primary factor or factor complex, the complex of all the 

 other genetic factors constituting the total heritage of the organism» 

 and the external environment. Changes in any one of these may 

 give rise to a new character or modify an old one, the distinction 

 between old and new being largely a matter of convenience, for, 

 when a factor still retains its usual or common expression, except 

 for slight modifications which do not alter its distinctive features, 

 it may still retain its old name, but when these changes in expres- 

 sion are so complete as to make their relation to the same factor 

 unrecognizable, it were better to describe them as new. This 

 interpretation is opposed to that conception of heredity which im- 

 plies dominance to be a possession of the factor or factors Prima- 

 rii}'' concerned in the inheritance of a character. On the other hand 

 it accords with and supports in every way, the fixed factor h} T po- 

 thesis, of East. Matouschek (Wien). 



Krau sei, R., Die Bedeutung der Anatomie lebender und 

 fossiler Hölzer für die Phylogenie der Koniferen. 



