404 Mr Gustav Mann on the 



all these preparations, we commence with the study of the 

 red end of the spectrum, gradually narrowing and widening 

 the slit of the collimator, and thereby modifying the amount 

 of light ; and when we have found the first band we have 

 to focus it very carefully with the collimating lens. Speak- 

 ing generally, I find that the red end of the spectrum 

 requires less and the blue end more light ; further, that in 

 the red end my band I, requires more light than my band 

 11. for proper definition, the band II. is apt to be " flooded " 

 with light just as prej)arations may be flooded in using 

 the microscope, and thus either rendered invisible or very 

 indistinct. 



Of all the higher plants I find Trichomanes renifornu', 

 a New Zealand fern, to give the most satisfactory results, 

 for the leaves are very transparent, due to the fact that the 

 mesophyll is only one layer thick towards the periphery; 

 hence in one leaf about 1^ inch broad one may study the 

 difference in the absorption between the paler peripheral and 

 the darker basal portion ; and further, the epidermis of the 

 leaf retains water for a long time, the latter not falling off 

 in drops ; and if several leaves have to be examined, the 

 water between the leaves lets us practically work as with 

 one single leaf. Being specially suitable, therefore, I shall 

 commence with the description of its absorption-spectrum. 



Trichomanes reniforme, Foster. 

 A. One leaf examined showed — 



1. A dark band, X 694 [centre at X 685] - X 677. 



2. A pale band, X 650 [centre at X 649] - X 648. 



3. A very faint band, X 490*5 [centre at X 484] - 



X 469-5. 



4. General absorption at X 446'3. 



The band No. 3 is a very faint absorption, and is best 

 seen by looking for a portion of the blue end of the spectrum 

 showing less absorption than the rest, lying about X 470 - 

 X 450, and then studying the area to its left. To see band 

 No. 3 well we must use all the light at our disposal. 



The general absorption at X 446*3 commences rather 

 abruptly, so as to give almost the impression of another absorp- 

 tion-band commencing here, but nothing definite can be 



