390 SCIENCE PROGRESS 



the relation of modern chemical and physical knowledge to 

 Cytological interpretation. It is pointed out that the most 

 important advances in our knowledge of cell architecture 

 have been the recognition of localised spatially differentiated 

 regions in which certain processes occur. The work on elaio- 

 plasts is particularly cited, whilst plastids, chromosomes, and 

 centrosomes furnish further examples. Attention is drawn 

 to the occurrence of almost every gradation from the undiffer- 

 entiated " chromatophore " of Hydrodictyon to the highest 

 types exhibiting not merely a well-delimited outline, but also 

 a special membrane. With regard to the relation of chron- 

 driosomes to the organised bodies of the adult cell, the opinion 

 is expressed that far more evidence is required than has so 

 far been adduced. 



The author proceeds to explain the structure of the cell 

 conceived as a polyphase colloidal system of complex chemical 

 compounds. Such a system, however, whilst consistent with 

 many observed facts, would, so far as we are aware, be devoid 

 of polarity and would exhibit an absence of the non-homo- 

 geneity which must be postulated for protoplasmic structure 

 in order to account for the diverse chemical processes which 

 proceed simultaneously within the cell. 



Our knowledge of multinuclear cells has been increased 

 by the account furnished by Beer and Arber (Proc. Roy. Soc), 

 who enumerate 1 1 7 species belonging to sixty families in which 

 such cells are present. These examples represent Pteridophyta, 

 Gymnosperms, Dicotyledons and Monocotyledons, and almost 

 every variety of vegetative organ. Most commonly to be 

 met with in the stem, this type of cell appears to be charac- 

 teristic of active tissues, and is regarded as a normal feature 

 in the growth of the majority of the higher plants succeeding 

 the meristematic phase. The power of division would appear 

 to be lost first by the cytoplasm and only subsequently by the 

 nucleus. By this means it is suggested that a more effective 

 relation between chromatic material and cytoplasm may be 

 maintained. In more than 100 species the several nuclei were 

 found to arise by mitotic division, but though this proceeds 

 normally up to the spindle phase and a cell plate is even 

 formed, this latter is resorbed and the daughter-nuclei 

 become enclosed in a hollow sphere which enlarges till it is 

 coextensive with the cytoplasm lining the cell wall. Sub- 

 sequently one or more of the nuclei may degenerate so that a 

 uninucleate condition is established. 



The Cytology of Nemalion multifidum has been studied by 

 R. C. Cleland (Ann. Bot.), who finds that there is no cytological 

 alternation of generations, but that, with the exception of the 

 first mitosis of the zygote, the chromosome number is eight 



