128 PRACTICAL BOTANY 



general arrangement of the tissues will be found the same, but 

 there are differences of detail, e.g. unicellular hairs of peculiar 

 spindle-form are found on both surfaces, there are three or more 

 layers of palisade-parenchyma, &c. 



Sections may also be cut with advantage from the leaf of the 

 Dahlia. 



Note on Chlorophyll Corpuscles, or Chloroplasts, and 

 Chlorophyll. 



These have already been described on p. 47 : the characters of 

 form, mode of division, and solubility of the green colouring 

 matter (chlorophyll) there noted should be verified on the chloro- 

 plasts of the Sunflower, or some other leaf. Chloroplasts which 

 have been bleached by alcohol should be stained with iodine, 

 when they will assume a brownish tint. 



If chlorophyll-corpuscles, which have been treated with picric 

 acid and decolorized with alcohol, be stained with iodine, Hoff- 

 mann's blue, or hsematoxylin, and be examined with a very high 

 power, it will be seen that they have a trabecular structure. The 

 leaves of Vallisneria afford good material for this observation. 

 The minute structure of the corpuscles can also be readily made 

 out in cells of the leaves of Echeveria. 



Solution of Chlorophyll in Alcohol, In order to prepare 

 this, a quantity of fresh grass or of cabbage-leaves 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 soaked in alcohol for some hours in a dark place. 

 When the alcohol is poured off and filtered, it will be found to be 

 deeply coloured, owing to the solution of the colouring matter 

 (chlorophyll), while the mass of leaves will be seen to be bleached. 



Take a small quantity of the solution in a test-tube, and 

 examine it first by light transmitted through it (i.e. hold it 

 between the window and the eye) : it will appear of a deep green 

 colour. Examine it now by reflected light (i.e. the observer is to 

 place himself between the window and the tube, so that his eye 

 receives light reflected from the tube), the solution will appear a 

 deep dull red : the solution is thus dichroic. 



