Comparative Study of Chlorophyll. 403 



Viva latissima. 



The absorption-spectrum of this alga is the following : — 



1. A dark band, X 694 [centre = X 682] — X 662. 



2. A pale band, its centre at X 650. 



3. A very pale band, centre at X 578"5. 



4. Absorption commencing at X 494. 



5. Most absorption about X 483. 



6. Very slight absorption, with its centre about X 452. 



As representatives of the vascular cryptogams and phanero- 

 gams types were chosen, with transparent leaves in which the 

 chlorophyll was not developed to such an extent as to render 

 the two bands in the red end of the spectrum confluent, or at 

 least in which the band commonly known as Kraus' band I. 

 showed distinctly a right darker and a left paler absorption, 

 the latter corresponding to my second band, when one leaf 

 was interposed between the direct sunlight or an Argand- 

 burner and the spectroscope. 



Leaves which have to be examined are arranged in a very 

 suitable way thus : — They are placed between two pieces of 

 blackened cardboard, in the centre of each of which is a 

 square hole about an inch and a half broad, in such a 

 way that when the two pieces of cardboard are put together, 

 the leaf fills up the hole entirely, and thus prevents any 

 light reachmg the spectroscope which has not passed through 

 its substance. The cardboard should be about twelve inches 

 broad, to prevent the examiner seeing the Argand-bumer, 

 for after one's eyes have seen a bright flame it is impossible 

 to do any fine spectroscopic work. If two sides of the card- 

 board are stitched together, about an inch from the margin 

 of the central hole, a leaf placed between them is held firmly 

 enough if the opposite side of the cardboards be fixed by a 

 clamp or test-tube holder. AVe arrange next the leaf thus 

 prepared in front of the spectroscope, and illuminate it by 

 cjoncentrating upon it the light of an Argand-bumer by 

 means of a condenser. With a soft, broad, and flat camel-hair 

 brush both sides of the leaf are wetted from time to time 

 to keep the leaf fresh ; and if we are working with two or 

 three leaves at the same time there should always be a layer 

 of water between the individual leaves, so that we may have 

 as little refraction of light as possible. After we have made 



