ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 363 



BOTANY. 



GENERAL, 



Including the Anatomy and Physiology of Seed Plants. 



Cytology, 

 including Cell-Contents. 



Chromosomes of Marchantia.* — J. H. Sckaffner has examined the 

 antheridiophores of Marchantia poiymorpha, and finds centrosomes in 

 the antheridial cells of all stages. At the commencement of nuclear 

 division, cytoplasmic radiations are to be seen on opposite sides of the 

 nucleus ; the centres of these radiations are the poles of future spindles. 

 In later stages asters are ill-developed, while in earlier generations they 

 are very conspicuous. The centrosomes are often surrounded by a 

 hyaline zone, and the aster forms a cloud-like halo. The centrosome 

 seems to enlarge in the grandmother-cells, and in the last division is 

 very clear and still more enlarged. The chromosomes of the gameto- 

 phyte are eight in number. After the final division the chromosome is 

 an oval, dark-staining body giving rise to flagella. The author con- 

 cludes that " the blepharoplast of Marchantia is only a skghtly modified 

 centrosome" traceable through many cell-generations, and probably 

 present through the entire ontogeny. 



Amitosis in Synchytrium.t — R. F. Griggs has examined nuclear 

 division in Synchytrium, and finds tkat tke numerous peculiarities 

 occur immediately after tke division of tke primary nucleus. Direct 

 division of tke nucleus occurs more frequently tkan mitosis, and is by 

 at least two processes, viz. — (1) nuclear gemmation, in wkich the 

 nucleolus separates off a small nucleolus, which passes through the 

 nuclear membrane, surrounds itself with a membrane, and forms an 

 independent small nucleus ; (2) heteroschizis, in which the nucleus 

 dissolves and the nucleolus breaks into many pieces, eack becoming a 

 new nucleus, eventually forming "a mornla-like cluster of nuclei." 

 Tke nuclei thus formed eventually undergo mitosis, and tkeir descendants 

 form spores. Tke number of ckromosomes in tke nuclei appears to be 

 constant. 



Structure and Development. 



Veg-etative. 



Thylose-formations.J — H. von Alten kas studied thyloses in 

 Manihot, Ficvs, etc., and draws the following conclusions from kis 

 observations. Tkere are two groups of tkyloses, distinguisked by 

 having a simple or compound membrane. Tke form and size are 



* Ohio Nat., ix. (1908) pp. 383-8 (1 pi.). 



t Bot. Gaz., xlvii. (1909) pp. 127-38 (2 pis.). 



% Bot. Zeit., lxvii. (1909) pp. 1-23 (1 pi and 4 figs.). 



