340 SUMMARY OF CURRENT RESEARCHES RELATING TO 



BOTANY. 



A. GENERAL, including the Anatomy and Physiology 

 of the Phanerogamia. 



a. Anatomy. 

 (1) Cell-Structure and Protoplasm. 



Framework of the Nucleus.* — HerrC. van Wisselingh has carefully 

 followed out the process of karyokinesis iu the embryo-sac of Lcncojum 

 and Fritillaria, and finds it to differ in some important points from that 

 which he has already described in the case of Spirogyra.^ After fixing 

 with Flemming's solution, the object was placed in 50 per cent, chromic 

 acid, in which tiie whole of tlie cytoplasm and the nuclear membrane 

 first of all dissolve, then the framework of the nucleus, and finally the 

 nuclei, leaving only the nucleolar threads. The following are given as 

 the more important results. 



The framework of the resting nucleus consists of lumps (Kliimpchen) 

 and granules, which are connected with one another by fine threads ; 

 there is no purely filamentous structure, and no distinction between 

 chromatin-threads and linin-threads. The knot-stage (Knauelstadium) 

 results from the union into threads of the lumps and granules ; the fine 

 connections between the lumps and granules contract ; the rest of the 

 fine connections mostly disappear. The nuclear threads become shorter 

 and thicker ; they run from the polar to the opposite side, and attach 

 themselves by their ends to the wall of the nucdeus ; they usually remain 

 more or less coiled. Kosettes or fan-like figures arise after the absorp- 

 tion of the nuclear wall ; the threads approach the polar region, and 

 become more firmly connected ; in other spots the fine connections 

 between the threads disappear. In the formation of the nuclear plate 

 the connection of the threads becomes looser, and their free ends bend 

 towards opposite sides. In the plate the united ends of the threads are 

 sharply curved, and lie in the equatorial plane. 



The nuclear threads are not, as stated by Strasburger, composed of 

 alternate plates of chromatin and linin, but of flattened lumps and 

 granules and fine contracted connections ; they show transverse lines 

 where the fine connections have finally contracted together. In the knot 

 stage the nuclear threads show a longitudinal striation. When the 

 nuclear plate is formed they split longitudiually, and the two halves 

 move in opposite directions towards the poles of the spindles ; the curved 

 ends remain united with one another ; the free ends turn inwards. In 

 Leucojum an exception to the curving is afforded in some of the 

 threads. 



When the halves of the nuclear plate have approached near to the 

 poles, the mutual connection of the threads becomes firmer ; they draw 

 together and form a dense knot, and are connected in many spots by 

 fine threads. They then again move apart, and run from the polar to 

 the opposite side. Gradually they break up into granules which are 

 connected with one another by fine threads. The wall of the nucleus 

 is formed round the framework, and the nucleoles make their appear- 



* Bot. Ztg., lvii. (1899) l te Abth., pp. 155-76 (1 pi.), 

 t Cf. this Journal, 1899, p. 186. 



