Cytologie und Befruchtung. jgj 



La spore müre de Ia Morille possede 8 noyaux. Celle du 

 Peltigera s'allonge secondairement comme celle du Phytlsma 

 puis se divise en 4 cellules uninucleees par un double cloisonne- 

 ment transversal. Paul V uillemin. 



Merriman, Mabel L., Vegetative Cell Division in Allium 

 (Botamcal Gazette. Vol. XXXVII. 1904. p. 178-207 Plates 

 11 — 13.) 



This is an extremely detailed account of nuclear division 

 in root tips of Allium. The illustrations are numerous, in very 

 close series, and are well drawn. 



The achromatic figure in Allium is derived from both 

 cytoplasm and nucleolus, the cytoplasmic fibrillae fusing with 

 the nuclear reticulum without the Intervention of „caps". Cen- 

 trosomes were not observed. Nucleoli are regarded as accu- 

 mulations resulting from the quantitative reduction of the 

 chromatin. 



In the earlier prophases the chromatin appears in the form 

 of a thread which is, at least, double and, perhaps, quadripartite. 

 In either case, the threads are soon seen to be quadripartite. 

 A chromatin granule might divide into two, and each of the 

 two into two more, thus forming the quadripartite thread, or, 

 possibly, the tetrad condition may be permanent, the granules 

 having an inherent tendency to group themselves into fours. 

 Up to the equatorial plate stage the chromatin shows growth, 

 aggregation, and fusion of tetrads into chromosomes; from the 

 equatorial plate stage to the formation of daughter nuclei there 

 is a disintegration of chromosomes into tetrads and a reduction 

 of the latter in size. After the fusion of the granules, the 

 chromosomes appear as tubulär structures, the tubulär character 

 being quite evident in transverse sections of chromosomes. 

 After the longitudinal Splitting, the daughter chromosomes are 

 tubulär at first but, in transverse section, soon show a resolu- 

 tion into the four granules of the tetrad, the longitudinal 

 appearance being that of a quadripartite thread. 



The number of chromosomes is not alway sixteen as de- 

 scnbed by other observers, but varies from ten to thirty or 

 more, the number depending upon the size and course of the 

 spirem in the nucleus. 



Miss Merriman believes that the second longitudinal 

 Splitting of the chromosomes, described by Strasburger and 

 others as characteristic of the heterotypic mitosis, is the same 

 pnenomenon as she described for typical mitosis in the root 

 tips of Allium. In other words, the mechanism of cell division 

 in both homotypic and heterotypic forms is essentially the 

 same - Charles J. Chamberlain (Chicago). 



