772 SUMMAEY OF CURRENT RESEARCHES RELATING TO 



disputes the assertion of Schmitz, Strasburger, and Tangl that the nucleus 

 is wanting in the PhycochromacesB. The presence of a nucleus was 

 demonstrated in the cells of Tolypothrix segagropila and Osciilaria sp. (in 

 the former it can be seen even in the living plant), while the cell-protoplasm 

 was found to be destitute of any substances exhibiting the reactions of 

 nuclein. 



The nucleins obtained from the yolk-spheres of animal ova differ in their 

 reaction from those of the nuclei of vegetable cells. They were obtained 

 from the frog, from Scyllium canicula, and from the hen. These agree in 

 their properties with the nuclein obtained from milk, and differ from those 

 now under consideration in not containing the elements of nitrogenous 

 bases, such as guanine, hypoxanthine, &c. In the vegetable kingdom 

 structures comparable to the yolk-spheres of animals have hitherto been 

 found only in the ovum-cells of Gymnosperms ; the author has found them in 

 Pinus sylvestris. 



In the resting condition the cell-nucleus consists of a matrix in which 

 the framework of the nucleus and the nucleoli are imbedded ; the former is 

 distinguished by containing nuclein; the latter consist of albumen and 

 plastin. If the albumen is removed from the nucleus by digestion, and the 

 nuclein dissolved in soda, a network remains behind consisting of plastin. 

 On the chemical nature of the matrix the author was unable to come to any 

 definite conclusions. 



As to the processes which take place during the division of the nucleus, 

 the author combats the statement of Strasburger of the intrusion of the 

 cell-protoplasm into the substance of the nucleus. Pollen mother-cells of 

 Hemerocallis fulva in the first stages of division before the disappearance of 

 the nucleolus, preserved in alcohol, showed after treatment with hydro- 

 chloric acid very clearly the matrix of the nucleus ; and this matrix does 

 not consist of cell-protoplasm, since it does not leave behind any residue of 

 plastin when treated with gastric juice. The same is the case also with 

 the spindle-fibres, which are stated by Strasburger to consist of cyto- 

 hyaloplasm. 



The author then discusses the changes which take place in the material 

 constitution of the nucleus and nucleoli during division. 



The nuclei of male sexual cells — those of the spermatozoa of animals 

 and of cryptogams, and the generative nuclei of the pollen of Gymnosperms 

 and Angiosperms — all exhibit essentially similar properties; they contain 

 a larger quantity of nuclein than the nuclei of vegetative cells, and either 

 smaller nucleoli or none at all. 



The nuclei of the male and female sexual cells differ materially in their 

 properties in the case of ferns (Pteris serrulata). The nucleus of the male 

 cell contains no nucleoli, and apparently consists of a homogeneous mags 

 composed essentially of nuclein. The nucleus of the female cell, on th^ 

 other hand, encloses large nucleoli and no nuclein, but a network or frame- 

 work exhibiting the reactions of plastin. The same is the case in MuscineeB, 

 and, to a less extent, in Gymnosperms. In the latter a similarity is 

 exhibited on the one hand between the nuclei of the canal-cells and the 

 spermatozoids, and, on the other hand, between those of the ovum-cell and 

 the vegetative nucleus of the pollen-tube. In Angiosperms the difference 

 between the nuclei of the male and female cells is less striking than in the 

 lower plants. In animals the same difference is presented between the 

 nucleus of the ovum and that of the spermatozoid before impregnation as 

 in the case of ferns and Muscinese. In both animals and plants the nucleus 

 of the male cell undergoes changes after its absorption into the female cell, 

 resulting in a close approximation to the nucleus of the latter. 



