C. H. OSTENFELD 121 



produced species-hybrids of the Pilosella subgenus we may find " apo- 

 gamic mutants " if we make the cultures extensive enough. And if this 

 supposition is right, it follows that we can declare the " apogamic 

 mutants" as being after-effects of earlier hybridization. 



In that way the contrast between Pilosella and Archieracium dis- 

 appears. Archieracium is then further advanced as regards apogamy, 

 and the microspecies of the present time are either the apogamically 

 seed-setting hybrids from the hybridization-period (as no fertilization 

 tackes place we must regard the apogamic propagation as a vegetative 

 propagation, a " klon "-propagation) or " apogamic mutants " arisen from 

 these. In both cases we find a basis of hybridization and in both 

 subgenera the real cause of the appearance of the many forms is the 

 hybridization, luhile apogamy is the reason that they keep constant. 



Another question is how this sudden appearance of single " apogamic 

 mutants " as after-effects of hybridization goes on. This is really a cyto- 

 logical problem which I can only touch very briefly. From extensive 

 studies of the cytology of the divisions in the pollen mothercells in 

 many Archieracium species Rosenberg (1917) has shown that there are 

 many irregularities. E.g. it happens that single chromosomes do not 

 follow the others in the regular movements during the division; we 

 may, so to speak, say that they are rejected or " forgotten." If we suppose 

 that something similar happens during the division of the embryosac 

 mothercell, it would be but natural to think that the " somatic eggcell" 

 in some cases gets a different number of chromosomes, e.g. one chromo- 

 some less than ordinarily. The embryo formed Avithout fertilization 

 from such a deviating " somatic eggcell " would produce a plant different 

 from the others derived from the same flowerhead, and in that way 

 we get an explanation of the appearance of the so-called " apogamic 

 mutants." This is of course only a mere hypothesis which has to be 

 proved by cytological investigation, but it is in agreement with the 

 experimental facts. 



LITERATURE. 



CoRRENS, C. (1905.) "Gregor Mendels Briefe au Carl Nageli, 1866—1873. Ein 



Nachtrag zu den veroflfentlichten Bastardierungsversuchen Mendels." Abh. d. 



math.-phifs. Kl. d. k. scichsischen Ges. d. Wiss. xxix. No. 3, 187—265. 

 Ernst, A. (1918.) Bastardierung als Ursache der Apogamie im Pflanzenreich. Jena 



(Gustav Fischer). 

 LoTSY, I. P. (1916.) Efolutlon by means of Hybridization. The Hague (M. Nyhoflf). 

 Massart, Jean. (1920.) "La notion de I'espfece en biulogie." Bull. Acad. roy. de 



Belg. des sciences, pp. 366 — 381. 



