130 



0)1 the Examination of 



Diagram of the Spectba of the Light transmitted thkough various Alg-je. 

 Ked end. Blue end. 



W X Y Z 



1. Palmella cruenta. 



2. Ked Floridea. 



Purple Floridea. 



Oscillatoria mrowTi in water. 



5. Oscillatoria (Microcoleus ?) 

 grown on a damp wall. 



(Fraunhofer's lines.) 



1. Palmella cruenta is a microscopic plant, closely allied to the 



so-called " red snow," found growing over the surface at the bottom 

 of damp walls, and looking as if blood had been spilt on the ground. 

 The spectrum may be seen by scraping off the external red part, 

 and keeping it for a while damp on thin glass, so that the red 

 granules may extend over the vacant spaces. It is, however, still 

 better to keep a quantity of the impure mass quite wet in a bottle, 

 when in the course of time the comparatively pure red material 

 will grow up the surface of the glass, and may be collected together 

 and examined on a piece of thin glass with concentrated sunlight. 

 The spectrum is characterized by the single well-marked band X. 

 "When the plant is kept in dilute bicarbonate of ammonia it is killed, 

 and the colour dissolved. It is a fine pink by transmitted Hght, 

 and gives the same absorption-band as seen in examining the plant 

 itself. This substance is extremely fluorescent, of orange colour, 

 giving a spectrum with a remarkably bright green-yellow band, 

 lying just on the red side of the band X in the transmitted hght, 

 and not coinciduig with it, as has been inaccurately said to be the 

 rule in such cases. This remarkably bright green-yellow band of 

 the fluorescence enables us to recognize this substance, even when 

 mixed with so much impurity that the absorption-band of the trans- 

 mitted light is almost or entirely hid. 



2. What I have named red Floridea is one of those normally 

 purple AlgaB which appear to tui'n red in a manner similar to the 



