462 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Amitosis in Parenchyma of Water-plants. — R. C. McLean gives 

 a brief description of amitosis in water-plants. The phenomenon has 

 been observed in the cortical parenchyma of eight genera, but is most 

 distinct and characteristic in Hippuris. In this genus amitosis occurs 

 in the reticulate trabecule of the cortex, and its occurrence follows the 

 general distribution of growth, being commoner in young stems than in 

 old ones ; it is also more frequent in the neighbourhood of a node than 

 in an internode, and is less common in the inner cortex than in the 

 outer. The irregular outline of the nucleus usually assumes a twisted 

 spindle-shaped form resembling the diatom Pleurosiyma, and the length 

 of such nuclei may be as much as ten or twelve times their diameter. 

 The separation of the daughter-nuclei is very slow, as is also the subse- 

 quent cell-division. Amitosis was the only form of nuclear division 

 observed in the tissues examined, and from its frequency it is probable 

 that no other form occurs there. The author has also discovered 

 amitotic division in the marsh-plant Dionsea muscipula and in the 

 epiphyte Polypodium ireoides, facts which indicate that the phenomenon 

 is of more frequent occurrence than has hitherto been supposed. It is 

 suggested that it may be the constant form of nuclear division between 

 sister-cells in all fully differentiated but still growing tissues, although 

 it may also occur in meristematic tissues. 



Evolution and Physiology of Mitochondrial — A. Guilliermond 

 publishes the concluding paper of his work dealing with recent cyto- 

 logical investigations as to the evolution and physiological function of 

 mitochondria. The author points out that there is abundant evidence 

 for regarding mitochondria as distinct organisms which elaborate the 

 products of secretion ; also, that the plastids of plants resemble and are 

 the products of slightly modified pre-existing mitochondria. The func- 

 tions of the latter are of a very general character, and there is no doubt 

 that the greater number of the secretory products of the cell are due to 

 their activity. It is now known that every animal and plant-cell 

 possesses a chondriome, which behaves exactly like a nucleus, in that it 

 divides during mitosis and its products are shared between the daughter- 

 cells ; the chondriomes are products of the mitochondria and possess 

 similar functions. Researches dealing with the mitochondria of animal 

 cells prove that their chemical composition is that of a lipoid (probably 

 a phosphatide) united to an albuminoid base ; this appears to be true 

 also in the case of plant-cells. 



The question of the physiological function of the mitochondria has 

 not been determined, but certain hypotheses based upon experiments 

 with animal cells point to important conclusions. Regaud, basing his 

 theory upon their chemical composition, maintains that they have a 

 selective power of intussusception, fixation, and concentration. This 

 theory finds support in the varied chemical reactions of plant-cells. 

 Mayer and Schaeffer propose a theory applicable both to animal and 

 plant cells and based upon three facts, viz. the universal presence of 



* Proc. Camb. Phil. Soc, xvii. (1914) pp. 380-3 (1 fig.), 

 t Rev. Gen. Bot., xxvi. (1914) pp. 182-208 (9 figs.). 



