ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 565 



BOTANY. 



GENERAL, 



Including the Anatomy and Physiology of Seed Plants. 



Cytology, 

 includine: Cell-Contents. 



Chromosome Structure in Plant-cells.* — Y. Gregoire has examined 

 the roots of Allium with special reference to the structure of the 

 chromosomes both in the state of rest and of division. The author 

 draws the following conclusions from his investigations : (1) At the end 

 of anaphase the daughter-chromosomes crowd round the pole, but without 

 fusing ; later on they separate, but are united at certain points. The 

 chromosomes undergo a gradual vacuolisation, so that the complete 

 network is a network of networks. During prophase this network 

 forms a series of spongy bands, which later on become homogeneous 

 ribbons ; the latter usually split longitudinally before metaphase, 

 although the splitting may be deferred. (2) The chromosome element 

 consists of an achromatophile substratum bearing a chromatophile sub- 

 stance. This latter is not in the form of corpuscles, neither can granules 

 be distinguished. During the later resting-stages, a granular appearance 

 is seen, but this is due to a massing together of the chromatophile sub- 

 stance, and not to independent granules. There is no reason for 

 believing that there are any such independent granules either in the 

 resting condition or during mitosis. (8) Longitudinal division consists 

 in the splitting of the chromosome ribbon, and not in the separation 

 of morphological units. (4) The chromosomes enter the quiescent 

 network independently during telophase, and leave it independently 

 during prophase. Everything points to the independence of the 

 chromosomes. 



Nuclear Division in Spirogyra.f — J. Berghs has investigated the 

 nuclear division in Spirogyra, with the purpose of discovering a general 

 scheme which will include the method of nuclear division Ijoth in the 

 higher and lower plants. The author finds that the nuclear network 

 is not chromatic, neither does it share in chromosome-formation. The 

 nucleolus contains all the chromatic elements, and does not disappear 

 during nuclear division. It has no membrane. The nucleolus is of a 

 twofold nature, and gives rise to twelve chromosomes which divide 

 lengthwise and are an-anged in an equatorial ring, while another sub- 

 stance of a different nature remains unchanged and preserves the form 



* La Cellule, xxiii. (1906) pp. 311-5G|(2 pis.), 

 t Tom. cit., pp. 55-86 (3 pis.). 



2 P 2 



