964 SUMMARY OF CURRENT RESEARCHES RELATING TO 



parenchyma of albinotized maple-leaves, &c., or from any non-chloro- 

 phyllaceous animal cells. Cells with a coloured cell-sap, but no 

 chlorophyll, as those of the hairs on the filaments of Tradescanfia 

 virginica, petals, &c., do not give off oxygen into the air. 



In all living cells, the evolution of oxygen takes place only at 

 those spots where the chlorophyll-grains lie ; and this is the case 

 even when the chlorophyll-bodies have retreated from the cell-wall. 

 Completely isolated chlorophyll-bodies of not more than 5 /x dia- 

 meter continue to give off oxygen, as may be plainly seen in Hydra 

 viridis and in many plant cells. The evolution proceeds even when 

 the surroimding protoplasm has been completely destroyed. Even 

 when a part of the chlorophyll-body has been destroyed, the remaining 

 portion continues to act ; but, as soon as its structure has been com- 

 pletely destroyed, the power of giving off oxygen ceases. The evolu- 

 tion is independent of currents in the protoplasm. Electrical 

 induction-currents, which caused contraction in Euglena, produced 

 no change in the evolution of oxygen. 



The phenomenon takes place at all periods of growth and of 

 cell-division ; the nucleus appears to have no influence upon it. 

 It seems to be absolutely dependent directly on the influence of 

 light. The ultra-red rays passed through a solution of iodine in 

 bisulphide of carbon, were found to be completely inactive ; while 

 the red rays of a wave-length between 0'70 and 0*60 /x were very 

 active ; the orange and yellow still more so ; the green rays were 

 the weakest ; the blue (below 0*50 /x) often considerably stronger. 

 There is no perceptible interval of time between the impact of the 

 light and the commencement of the development of oxygen ; and the 

 latter appears to cease the moment the former is withdrawn. 



Micro-photography.* — At the Brieg meeting of the Swiss Natural 

 History Society, Dr. Du Plessis exhibited some micro-photographs 

 of Hydroids — negatives on glass for projection — at the same time 

 lamenting that the numerous technical difficulties produced disap- 

 pointments which discouraged naturalists, although micro-photo- 

 graphs were of extreme importance both on account of their faithful- 

 ness and their usefulness for class instruction. M. His, however, 

 contended that the discouragement arose primarily from the fact that 

 proper objects were not selected, all microscopical objects not being 

 suitable for photographing. The most unfavourable objects were often 

 first selected, and there was always a temptation to employ too high 

 powers. Only those objects should be used which can be observed 

 with low powers, and especially those which give stereoscopic images. 



Histology and Microscopy. — Microscopists have for many years 

 insisted that it is absolutely essential that histologists should be 

 grounded in the theoretical principles applicable to the instrument 

 with which they work, and, that if this is not done, not only will 

 erroneous interpretations of structure be put forward, but many points 

 of importance will be altogether missed. 



* Verh. Schweiz. Naturf. Gesell., Ixiii. (1881) pp. 39-41. 



