ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 915 



one with abundant protoplasm containing a single nucleus, nucleolus, 

 and endonucleus ; a cell with vacuolated protoplasm, one nucleus, and 

 two to four nucleoli is less exalted ; the multinuclear state is most 

 degraded." 



Structure and Division of the Nucleus.* — L. Guignard has re- 

 investigated the phenomena connected with the division of the cell- 

 nucleus in the mother-cell of the pollen-grains, and in the ovary ; 

 the plants examined being chiefly monocotyledons — Lilium Martagon, 

 Allium ursimim, Alstroemeria pelegrina, Listera ovata, and others. At 

 the time of division the nucleus is invested with a delicate membrane 

 which behaves to reagents in the same way as the microsomes of the 

 cytoplasm surrounding the nucleus. It is coloured by carmine and 

 hfematoxylin, while safranin scarcely reveals it ; with slightly acidu- 

 lated methyl-green it presents a double contour and a much more 

 pronounced staining than the cytoplasm. 



The author agrees with Strasburger — contrary to the opinion of 

 Flemming — that when the nucleus is at rest it contains a single 

 continuous filament, which, with the nucleoli, contains all the chro- 

 matin of the nucleus. At the moment of division the nucleoli 

 disappear, the filament contracts, and then divides into a certain 

 number of rods ; these rods curve on themselves, and the two parts 

 thus defined become more and more closely attached to one another ; 

 they then arrange themselves in a plane and form the nuclear plate. 

 Almost at the same moment the membrane of the nucleus disajipears, 

 and the achromatic filaments then make their appearance, arranging 

 themselves in the form of a barrel. In the next stage the rods divide 

 longitudinally, and each of the halves moves to one pole of the barrel 

 formed by the achromatic filaments. The filaments at each pole then 

 unite end to end, and form the nucleus of a daughter-cell, going 

 tbrough in inverse order the series of transformations which took 

 place in the nucleus of the mother-cell. The origin of the achromatic 

 filaments he regards as still obscure. 



Guignard regards the nucleoli not simply as denser parts of the 

 substance of the nucleus, but as a special product of its metamorphosis 

 and of the vital activity of the nucleus. They are not invested by a 

 membrane, and are readily distinguished by their optical properties 

 and their receptivity to staining, from the chromatic substance of the 

 nucleus. In Listera ovata, htematoxylin stains them entirely a yellow 

 red, while the filament becomes dark violet. 



Formation of Endosperm in Daphne.f— E. Strasburger contests 

 the statement of Prohaska X as to the formation of free nuclei in the 

 embryo-sac of Dajjhne Blagyana. He asserts that the structures 

 described by Prohaska as free nuclei are not found in the parietal 

 protoplasmic layer. 



* Ann. Sci. Nat. (Dot.) xvii. (1881) pp. 5-59 (4 pis.). Cf. this Journal, iii. 

 (1883) p. 861. 



t liiT. Dculsch. Dot. Geaell., ii. (1884) pp. 112-4. 

 j Kcc this Journal, ante, p. 250. 



