548 SUMMARY OF CURRENT RESEARCHES RELATING TO 



BOTANY. 



A. GENERAL, including the Anatomy and Physiology 



of the Phanerogamia. 



o. Anatomy. 



CI) Cell-Structure and Protoplasm. 



Movements of Nuclei.* — M. Kornicke confirms the correctness of 

 his previous observations that, under certain conditions, nuclei have 

 the power of passing through the cell-wall. In the case of the large 

 nuclei of the pollen mother-cells of Crocus this is effected by means 

 of the protoplasmic connections which are clearly shown by treatment 

 with chromic acid, both in the state of rest and in division. In the 

 first case, when a nucleus approaches a cell-wall, protrusions take place 

 through the pores. The portions which pass through often again unite, 

 so that a normal nucleus is formed, passing through the cell-wall. The 

 nucleole usually remains in the older cell. Sometimes the nuclei occu- 

 pied a central position, but had protrusions with rounded ends, or a 

 portion of the nuclear thread projecting into a neighbouring cell. Con- 

 nections were thus frequently established from cell to cell. All the 

 cells in a pollen-chamber would sometimes exhibit this partial passage 

 of nuclei. A complete passage was never observed. 



Centrosome-like Structures in the Vegetative Cells of Vascular 

 Plants. | — B. Nemec has observed, in many cases, in the vegetative cells 

 of the higher plants, during the process of nuclear division, structures 

 which bear a strong superficial resemblance to centrosomes. These he 

 divides into two classes: — (1) Structures which occur also in resting 

 cells, and which lie, in nuclear division, at the poles of the achromatic 

 figure (Diplaziurn pubescens, Blechnum brasiliense) ; (2) Structures of 

 which no trace is to be found in the cytoplasm of the resting cell, but 

 which appear as the poles of the fully developed achromatic figure, and 

 disappear when the reconstruction of the daughter-nucleus is completed. 

 These latter include three kinds of corpuscles : — Structures which are 

 differentiated in the cytoplasm directly at the poles of the achromatic 

 figure at the end of prophasis, and exhibit no demonstrable genetic 

 relation to the nucleoles (Dracaena arborea); and corpuscles which arise 

 at the poles by the transformation of achromatic fibrillaB at the end of 

 metakinesis, and have the appearance of small roundish nucleoles 

 (Allium) ; or appear in the iorm of thick irregularly circumscribed 

 masses of protoplasm after metakinesis is completed (pollen mother- 

 cells of Nymphsea alba). 



Structures of the kind under consideration may appear in resting 

 cells. Those which appear in ferns bear the strongest resemblance to 

 true centrosomes. They are usually solitary and of irregular form. 



* SB. Niederrhein. Ges. Nat. u. Heilkunde, Bonn, 1901. See Bot. Ztg., Ii\. 

 (1901) 2"> Abt., p. 187. 



t Ber. Deutsch. Bot. Ges., xix. (1901) pp. 301-9 (1 pi.). 



