( 269 ) 



again. The thick thread now divides transversely into L4 chromosomes, 

 the nuclear wall disappears, and the chromosomes place themselves 

 perpendicularly lo the long axis of the spindle of the heterotypic 

 division. h\ the synapsis of Oen. Lam. no double tfwead can therefore 

 be seen; from that thread ilie vegetative number of chromosomes is 

 formal, and just before the division these chromosomes shorn pairing. 



Both in the ovules and in the stamens the synapsis takes place 

 in this manner. In the first division of the mother-cells entire 

 chromosomes separate, which already during this division show a 

 longitudinal splitting for the second division. After this heterotypic 

 division the two nuclei scarcely enter upon a stage of rest, the 

 chromosomes, split longitudinally, always remain visible, especially 

 in the mother-cells of the embryosac. The wall het ween the two 

 nuclei is often not formed completely. At the second division the 

 halves of the two chromosomes separate, so that 4 nuclei are formed ; 

 in general hut little staining substance is visible 1 ). 



Whereas in most plants the lowest-cell of the tetrad grows out to 

 form the definitive embryosac, this is not so in Oen. Lom. Here 

 the uppermost cell becomes the embryosic, while the other three 

 degenerate; the chromatin of these three cells quits the nucleus, of 

 which the wall disappears, and the chromatin now colours the whole 

 protoplasm dark, so that these three cells of the tetrad remain visible 

 for a long time as a long dark band under the embryosac. In that 

 cell of the tetrad, which grows out, three successive divisions take 

 place in almost all plants, so that 8 nuclei are formed. In Oenothera 

 I always found but 4 nuclei, which come to lie in the upper part 

 of the embryosac. A limited number of nuclei is also known in 

 Helosis guyanensis, in consequence of the researches of Chodat and 

 Bernard 8 ) and in Mour-ra, through an investigation of Went 3 ). 

 In these plants the lower of the two nuclei, which are formed in 

 the first division, probably degenerates; from the upper nucleus the 



l ) In the May meeting of the Dutch Botanical Society, in which I dealt with 

 the greater poition of this subject, I already slated thai tin' synapsis in Oen. Lam. 

 takes place in this manner, thereby differing from what has heen stated to occur 

 in other plants. As I found in the beginning of September there appeared in the 

 July number of the Botanical Gazette a paper by Gates on the synapsis and reducing 

 divisions in the pollen mother-cells of Oenothera rubrinervis. This observer gives 

 much the same succession of stages for the synapsis of this plant. 



-) R. Chodat ct G. Bernard. Sur Ie sac embryonnaire de V Helosis guyanensis. 

 Journal de Botanique T. XIV, I £00 p. 72. 



: i F A. V. (!. Went. "The development of the ovule embryo-sac and egg in 

 PodostewittCMe" Recueil des Travaux Bolaniques Neerlandais, Volume V, Livraison 

 I, 1908. 



18* 



