620 SUMMARY OF CURRENT RESEARCHES RELATING TO 



BOTANY. 



GENERAL, 

 Including the Anatomy and Physiology of Seed Plants. 



Cytology, 

 including- Cell-Contents. 



Mitosis in Synchytrium.* — F. L. and A. C. Stevens have studied 

 the behaviour, during division, of the primary nucleus of S. decipiem 

 which invades single cells of the hog peanut. The nucleus attains to a 

 very large size, having a diameter of 35 /x with a nucleolus over 11 ^ 

 across. The nuclear wall is very distinct and the chromatin is collected 

 on the wall and around the nucleolus. The first sign of division is the 

 vacuolisation of the nucleolus, then the membrane loses its sharpness, 

 becomes gelatinous and finally disappears, though the outline of the 

 nucleus is not lost. A spirem condition of the chromatin is meanwhile 

 produced by the globules of the coarse and lumpy chromatin becoming 

 elongated and forming threads which are crossed and tangled in inex- 

 tricable confusion. During these stages the nucleolus disappears and 

 the nucleus becomes much shrunken, being often reduced to half its 

 diameter. The threads of the spirem group then gradually form a 

 small spindle which lies in the middle of the nuclear area but does not 

 extend to its periphery ; the spindle shows no centrosomes or radiations. 

 On the spindle only a few short chromosomes are found so that a great 

 condensation or an actual reduction of the chromatin must take place. 

 The chromosomes are apparently four in number and after their polar 

 migration the spindle lengthens, as in Albugo Bliti, and the telophase 

 is similar to that described for that form. 



Mitosis in Pellia.f — C. J. Chamberlain in his investigation deals 

 with the first two nuclear divisions in the germinating spore. For com- 

 parison, however, mitosis was studied in other phases of the life-history. 

 The principal conclusions are as follows. The stimulus to nuclear 

 division comes from within the nucleus. The asters are of cytoplasmic 

 origin. The caps come from the outer portion of nuclear membrane 

 or from a Hautschicht surrounding the nucleus. The appearance and 

 disappearance of the astral rays suggest that they are concerned in the 

 movement of nuclear matter. The centrosphere is formed by the astral 

 rays, not the rays by the centrosphere. The centrosphere of Pellia 

 represents a condition intermediate between the well-defined centro- 

 sphere of some of the tballophytes and the centrosomeless condition of 

 the higher plants. The spindle-fibres, except the mantle-fibres, grow 

 from one pole to the other. In early stages two half-spindles are often 

 distinguishable. 



* Hot. Gazette, xxxv. (1903) pp. 405-14 (2 pis.). 



t Reprint from the University of Chicago Decennial Publications, series 1, x. 

 (1903) 18 pp., 4to. The University of Chicago Press, Chicago, Illinois. Also Bot. 

 Gazette, xxxvi. (1903) pp. 28-51 (3 pis.)- 



