822 SUMMARY OF CURRENT RESEARCHES RELATING TO 



without any nuclein ; but it is improbable that the latter contain 

 plastin. They have a still closer affinity with the starch-generators 

 in the epidermal cells of flowering plants, plastin being certainly 

 present in these also. But the albuminoids of the starch-generators 

 display different reactions from those of the nucleoli, deliquescing in 

 water. 



The nucleoli always disappear when the nucleus is about to 

 divide ; their disappearance and reappearance in the daughter-cells can 

 be peculiarly well watched in living cells of Chara, especially in the 

 growing apices of the rhizoids. In one instance the whole process of 

 the division of a nucleus, and that of its daughter-nuclei was followed 

 in the course of twenty-four hours. The nucleolus of the living 

 nucleus is not homogeneous, but contains vacuoles varying in number 

 and size; and the different parts also display different degrees of 

 refringency. When the nucleus is about to divide, the nucleolus 

 loses its sharpness, and undergoes slow and finally amcBboid changes 

 of form, at length entirely disappearing. At a later period several 

 fresh nuclei are to be seen in the daughter-nuclei ; and these almost 

 immediately coalesce into one. During the coalescence these new 

 nucleoli lose their sharpness, which they again rapidly regain later. 

 The author has been unable definitely to determine what becomes of 

 the substance of the nucleolus after its disappearance, and its re- 

 lationship to the elements of the nuclear plate and to the spindle- 

 fibres. Possibly the albuminoid substance only disappears, the frame- 

 work of plastin remaining and passing into the daughter-nuclei, 

 where it again takes up albuminoids. 



Zacharias regards the statements of Strasburger and others as to 

 the appearance of so-called " paranucleoli," and their expulsion from 

 the nucleus, as resting on error, resulting partly from the esclusive 

 use of hardened material. 



The behaviour of the nucleoli is somewhat different in male and 

 female sexual cells. While they are invariably present in the latter, 

 they may disappear from the former before their complete develop- 

 ment. This difference was displayed in Chara, Marchantia, and in 

 several ferns. In the oosphere of flowering plants a nucleolus 

 appears never to be wanting ; while in the nucleus of the pollen-cell 

 it is not to be detected immediately before impregnation. In the 

 nucleus of vegetative cells it is always present. 



No general statement can be made with regard to changes in the 

 nucleolus as the cell becomes older ; it seems sometimes to increase, 

 sometimes to decrease in size ; in some cases it undergoes alteration 

 in form, while in other cases no change is apparent. 



The author is unable to assign at present any physiological 

 function to the nucleolus. At the same time he dissents from the 

 view of Strasburger, Carnoy, and Pfitzner, that it is not the living 

 substance of the nucleus, and can only be regarded as a reserve- 

 substance. 



Chlorophyll and its Combinations.* — Some investigations of 

 M. Guignet seem to show that chlorophyll is contained in envelopes 



* Comptes Rendus, c. (1885) pp. 434-7. 



