NOTES. 217 



structure of the pupa must necessarily be taken into consideration 

 before a satisfactory system of classification is arrived at, and Dr. 

 Chapman's views will probably afford material for considerable 

 discussion. It is not so many years since the genus Psyche was 

 removed from the Bombyces (where it formed a striking contrast 

 to the giant Saturfiias) and placed in the micro-lepidoptera. 



Mr. T. Mellard Reade, in the Geological Magazine for March, 

 supplies the latest computation as to the age of the earth. He 

 says : — " The mean area of denudation throughout post-Archaean 

 times being taken as one-third the entire land-areas of the globe, 

 the bulk of the post-Archaean rocks being expressed by the land 

 area of the globe two miles thick, and the rate of denudation one 

 foot in 3,000 years ; the time of accumulation will be 5280 x 2 

 X 3000 X 3 = 95,040,000. The time that has elapsed since the 

 commencement of the Cambrian is, therefore, in round figures 95 

 millions of years ^ The italics are Mr. Reade's. 



At the February meeting of the R.M.S., the Rev. Dr. VV. H. 

 Dallinger, in discussing Mr. Nelson's paper on the chromatic 

 curves of microscope lenses, pointed out that unless some means 

 could be devised to allow of the employment of the shorter wave- 

 lengths of the spectrum, we had nearly reached the limits of visual 

 possibility with the means at present at our disposal. He also 

 considered that there could be little doubt that all who believed in 

 the advantage of monochromatic light foresaw that there must be 

 lenses specially prepared for its use. 



Electric Light and Plant Structure. — G. Bonnier has 

 conducted some interesting experiments to ascertain how the 

 structure of herbaceous plants is influenced by exposure to the 

 electric light. He finds that direct electric light is prejudicial to 

 the normal development of the tissues on account of its ultra- 

 violet rays. Generally, when considerable development, accom- 

 panied by intensification of the green colouration, is caused by 

 continuous electric light, in plants growing under glass shades that 

 intercept excess of ultra-violet radiation, at first high diff'erentiation 

 occurs in the structure of the organs ; but an intense light, pro- 

 longed unchanged for months, causes remarkable modifications of 

 structure in the various tissues of such new organs as are capable 

 of adapting themselves to the illumination. Less difterentiation 

 then takes place in these organs, though they are always rich in 

 chlorophyll. — Co??iptes Rejides. 



