140 NOTES AND MEMORANDA. 



duction of carbonic acid. If we prevent it from reaching tlieleaf, • 

 the plant being reduced to consume the reserves previously accumu- 

 lated, becomes exhausted, and iinally dies. 



But though this part of the spectrum is necessary to plant life, it 

 cannot be said that it is sufficient. Behind red glass, plants live a 

 very long time, no doubt, but they become elongated to excess, and 

 slender, with their leaves narrow and pale-coloured, because they are 

 deprived of the violet blue rays. 



Thus every part of the solar sijectrum contains portions which 

 play an active role in the life of plants. In the most refrangible rays 

 are found those which govern the destruction of tension. In the red 

 are those which determine the tension of the tissues and produce the 

 phenomena of reduction, which are the foundation of vegetable life. 

 Their total, properly proportioned in white light, is necessary for 

 the vital harmony. 



It is very probable that these parts utilizable by plants are 

 accurately marked by the difiFerent absorption bands of chlorophyll ; 

 but to be quite sure, we should have to experiment with luminous 

 spectra, intercepting the different parts by screens, and recomposing 

 by means of lenses. The bad weather last summer did not allow 

 M. Bert to operate with the solar spectrum, and he accordingly made 

 arrangements for using a strong electric light, the results of which 

 have not yet been published. 



Colonel Woodward on the Oil- Immersion Objectives and the 

 Apertometer. — Colonel Woodward has examined the i and -^^ objec- 

 tives made by Mr. Zeiss, on what Professor Abbe terms the " Stej^hen- 

 son homogeneous immersion system," and thus reports upon them : — 



" My first trial by lamplight immediately convinced me of the 

 excellent quality of the |^ and of the surpassing excellence of the -^^. 

 On testing them by monochromatic sunlight, using a microscope 

 body with draw-tube, by which I could get ten inches precisely 

 with a range of a couple of inches either way, I speedily satisfied 

 myself that the performance of the ^ fully equalled, while the ^ ex- 

 celled, the best of the large collection of immersion objectives belong- 

 ing to the Museum. For photographic purposes the objectives gave 

 similarly satisfactory results. 



I find that the saving of time in using these oil-immersion 

 objectives on histological preparations mounted in balsam, and in all 

 similar work, is very great. With water and even glycerine immer- 

 sion objectives every conscientious worker loses much time with the 

 cover adjustment, and this is entirely economized, while the results, 

 instead of being inferior, are superior to any obtainable with the best 

 objectives made on any other principle." 



Colonel Woodward's measurement (by a method of his own) of the 

 aperture of the objectives gave 115° interior angle for the ^ and 114° 

 for the ^. By the apertometer he made the angle of each a little 

 more than 1 • 25 (numerical aperture). In regard to the scale of the 

 apertometer. Colonel Woodward considers that it has, among other 

 inconveniences, this, that its divisions are too far apart for any very 



