260 Cytologie und Befruchtung. 



Dans le premier de ces memoires, Berghs etablit la con- 

 clusion du memoire pr^cddent de Gregoire, au sujet de la 

 2« ötape de la F""^ Periode. L'auteur montre que ies chromo- 

 somes-fiiles I sonl bien Ies „moities longitudinales" des tron9ons 

 spirematiques. 



Dans Ies trois autres m^moires, Berghs etudie le synap- 

 sis, II montre que le reseau chromosomique quiescent se trans- 

 forme d'abord en des filaments minces, qu'ensuite ces fila- 

 ments minces se conjuguent deux ä deux, qu'ainsi se forme 

 le spireme epais dont le „dedoublement longitudinal" n'est pas 

 autre chose que la reapparition des filaments associes. Ces 

 phenomenes presentent un peu de variete d'apres ies differents 

 objets. Le Drosera offre Favantage de montrer des conjugai- 

 sons entre filaments minces ä un stade tres primitif, ä un 

 moment oü le reseau chromosomique n'est pas encore com- 

 pletement transforme en filaments minces. 



L'auteur confirme le memoire de Gregoire (04) et se 

 rallie ä la these de la prereduction. v. Gregoire. 



Christman, A. H., Sexual Reproduction in the Rusts. 

 (Bot. Gazette. Vol. XXXIX. 1905. p. 267—275. Plate 8.) 



This study deals with the origin of the binucleated con- 

 dition found in the aecidiospores of the rusts. The principal 

 forms investigated were Caeoma nitens S. growing on a culti- 

 vated species of Riibiis, and Phragmidiiim speciosum Fr. gro- 

 wing on Rosa hiimilis. These forms are particularly favorable 

 for cytological investigation on account of the large size of 

 their nuclei and cells. 



In Phragmidiiim the entire history was traced from the 

 uninucleated mycelial cells to the binucleated aecidiospore. As 

 the young pustule develops, terminal cells of hyphae become 

 enlarged and elongated in a direction perpendicular to the 

 epidermis. A nuclear and cell division now takes place cutting 

 off a small distal cell which degenerates. The free ends of the 

 larger remaining cells, or gametes, then come together in pairs, 

 the cell walls at the point of contact are dissolved and the 

 cytoplasm of the two cells becomes continuous, but the two 

 nuclei do not fuse. The nuclei now divide by conjugate divi- 

 sion, forming the first aecidiospore mother-cell, which is 

 binucleated. The aecidiospore mother-cell divides into twa 

 unequal cells, the aecidiospore and a small intercalary cell. 

 The conjugated portion grows in length and more aecidiospore 

 mother-cells are formed in the same way. Thus there is a 

 fusion of gametes at the base of each row of aecidiospores, but 

 the nuclei do not fuse, and the cell produced by fusion germi- 

 nates at once. 



In Caeoma nitens there is the same division into sterile 

 cells and gametes, and the double origin of the row of aecidio- 

 spores is evident 



