102 GENETICS [Bot. Absts., Vol. VI, 



Linnean species Chrysanthemum leucanthemum L.] Genetica 1: 401-442. Sept., 1919. — Bio- 

 metric measurements of length and breadth of ray-flowers made very probable, that the 

 Linnean species Chrysanthemum leucanthemum L. contains several strains of hereditarily 

 different character, in this sense, that this "species" is a mixture of types, differing in inherit- 

 able qualities, and their respective hybrids. — By systematic breeding and counting the ray- 

 flowers of a number of plants grown in families, it could be proven, that this supposition was 

 right and that this Linnean species is far from a unity, but a mixture of types and hybrids. 

 This makes it possible to grow out of this species a number of families, differing in hereditary 

 characters, among others those relating to the number of ray flowers; these families seem to 

 have the Fibonacci-numbers 21 and 34 as modes. — .1/. J. Sirks. 



1125. Sirks, M. J. Die kritische punten van het evolutievraagstuk. [Critical points of 

 the evolution hypothesis.] Genetica 1: 70-91. Jan., 1919. — The problem of evolution is by 

 most authors taken as a whole; in reality it may be analysed and divided in four great prob- 

 lems, that are more or less favorable to experimental research, the only right way for finding 

 an answer free from speculations. These four critical points out of the mass of problems are: 

 — (1) The origin in nature of new forms, in hereditary factors varying from their parents; 

 experimental research has thus far only shown one cause of this origin: hybridization, that is, 

 fusion of gametes differing in hereditable properties. All other ways of origin of new forms 

 have been thus far unproven. — (2) The existence in nature of groups of individuals, charac- 

 terized by possessing a great complex of hereditary factors. Answering this problem has been 

 till now unexperimental; mathematical considerations may show the necessity of divergence 

 of a very complicated population into different strains of homozygotic individuals, but also 

 circumstances of life, — isolation, dying out of certain forms and perhaps influence of circum- 

 stances on hybrid-splitting — may cause the differentiation of a population into different 

 strains. In this direction a great and extensive field of experimental labor is to be done, 

 before a well-founded answer can be given. (3) The dying out of forms and of groups of forms 

 is more a historical problem; perhaps it will be possible, by means of submission of populations 

 of known genetic constitution to various circumstances of life. — (4) Is there in natural evolu- 

 tion a progression or only a succession? This is a problem of a very subjective character; 

 it is wholly inaccessible for experiments and will remain in the long future a point of philo- 

 sophical discussion. — M. J. Sirks. 



1126. Sirks, M. J. Raszuiverheid en fokzuiverheid. [Purity of race and purity of breed- 

 ing.] Genetica 1: 539-552. Nov., 1919. — In genetics every word and every term has gone 

 through its own evolution; this brings in many cases great difficulties for obtaining an exact 

 definition of each of these terms. Every term changes its meaning with the changes of ge- 

 netics itself; they become more and more sharpened or they must be banished from the 

 geneticists terminology. A discussion of the terms purity of race and purity of breeding is 

 given here by the writer. In pre-Mendelian times identity of portrait (description of figure) 

 could be accepted as indicating purity of race: the Galtonian theory has changed this stan- 

 dard into identity of ancestry, and Mendelian researches have given as definition of purity of 

 race identity of posterity. The exact geneticist would go farther and take as definition 

 the identity of the gametes, formed by an individual as standard for purity of breeding. In 

 practice it is not yet possible to accept this sharpest definition; there are cases, that an indi- 

 vidual gives a posterity, seemingly identical, without forming only one sort of gametes. These 

 cases are treated by the writer in detail: the case of the white mice, among others, the case 

 of apogamy in plants without reduction-division and the case of eliminating of the homozy- 

 gote combinations as in yellow mice and in Oenothera-species. — A method of determining the 

 purity of breeding in cases where direct experiments are difficult, is indicated by Schmidt of 

 Copenhagen by his method of diallel (cross-wise) matings. — M. J. Sirl:.s. 



1127. Sirks, M. J. Verwantschap als biologisch vraagstuk. [Relationship as a problem 

 of biology.] Genetica 2: 27-50. Jan., 1920. — The problem of relationship has always taken a 

 central position in genetics; its analyses along the lines of modern genetics is a subject of 



