62 M. Pringsheim on the Action of Light 



Downtonian Strata. 



Above the horizon of the Aymestry Limestone, which forms 

 the divisional line between the Lower and Upper Ludlow 

 groups of Murchison, no distinct species of Graptolite has yet 

 been identified. Prof. Phillips * notices the presence of 

 Graptolites in the Upper Ludlow of the Malvern Hills, but 

 does not attempt their identification. Mr. R. Etheridge f 

 catalogues a fragment of a Graptolite from the supposed 

 Lower Old Red Sandstone of Lanarkshire. Mr. G. Linnars- 

 son informs me that he has recently recognized a Graptolite 

 ill a collection of fossils from the Gothland Sandstone, which 

 possibly corresponds to the lower part of the British Down- 

 tonian series. 



[To be continued.] 



VI. — On the Action of Light and the Function of Chloro- 

 phyll in Plants. By M. Pringsheim J. 



My purpose in this preliminary communication is to state 

 some results which I have obtained by a new and peculiar 

 method of investigation in concentrated sunlight. 



I have made use of this method for some years in order to 

 gather experimental knowledge of the relations of light to the 

 absorption of gases by growing plants, and of the part played 

 therein by chlorophyll. Amid the confusion of contradictory 

 opinions and statements which pervade the literature of the 

 subject, after many vain endeavours to advance upon the path 

 usually trodden, I felt myself bidden to proceed to the employ- 

 ment of intensified light. I hoped thus to be able in a short 

 time to bring into view, and unequivocally to observe imme- 

 diately in the cell, and directly under the microscope, the 

 processes called forth in plants by the action of light. 



In fact the experiments which have hitherto been made 

 have laboured under the serious defect that too inconsiderable 

 intensities of light were employed. This is especially true of 

 those experiments in which it was endeavoured to prove that 

 the different colours of the spectrum act differently upon 

 plants. If plants are grown in diffused daylight, or even in 

 direct sunshine behind coloured screens or coloured glasses or 



* Phillips, Mem. Geolog. Survey, vol. ii. 



t Etheridge, Mem. Geol. Survey Scotland, Explan. Sheet 23, p. 57. 

 % Translated from the ' Monatsbericht der koniglich preussischen 

 Akademie der Wissenschaften zu Berlin,' July 1879, pp. 532-546. 



