42 PRACTICAL BOTANY. 



be prepared. A quantity of fresh grass is to be taken 

 and freed as far as possible from decayed leaves ; it is 

 then to be boiled in water, pressed so as to get rid of 

 as much water as possible, and spread out on a sheet of 

 paper to dry in a dark place ; when dry it is to be put 

 into a flask and alcohol is to be poured over it, and it is 

 to be left for some hours in a dark place. When it is 

 seen that the alcohol is coloured green, it is to be poured 

 off and filtered ; the solution is now ready for use. 



The following is a convenient mode of examining 

 the solution spectroscopically : The tube of a microscope 

 is withdrawn (this may be easily done with the smaller 

 forms of Zeiss', Hartnack's, and Crouch's microscopes), 

 and it is replaced by a glass tube, the bottom of which 

 covers the opening of the stage of the microscope ; the 

 sides of the tube must be made opaque by wrapping 

 round them a sheet of black paper ; the solution is then 

 poured into the tube, and into the opening of the tube 

 a microspectroscope is introduced ; the mirror of the 

 microscope is to be so inclined that it reflects a beam 

 of light onto the bottom of the tube. The advantage 

 of this method is, that it enables the observer to vary 

 the thickness of the layer of the solution to be 

 examined. 



It is best to use a dilute alcoholic solution. Beginning 

 with a column of the solution about f of an inch in 

 height, the spectrum will present a single rather narrow 

 absorption band (band I.), in the red, about the line 

 of the solar spectrum, extending towards B\ if the 

 height of the column be about doubled, band I. will be 

 seen to have become broader, a faint narrow band 

 (band II.) will be seen to the right of it, between the 



