30 PRACTICAL BOTANY 



under the microscope : they will be found to have lost their 

 high refractive power. Stain with iodine : they give a pale 

 blue or yellowish colour. 



IV. Chloroplasts, or chlorophyll-corpuscles. 



Mount a fresh Fern prothallus in water, and note as in the 

 last chapter the several parts of the cells which compose it, and 

 especially the green chlorophyll-corpuscles, which are usually 

 of discoid form, sharply defined from the surrounding colourless 

 protoplasm. 



Observe here and there granules of oval or biscuit-shaped 

 outline : these are stages in the process of division, by which 

 means the chlorophyll-corpuscles increase in number. Draw- 

 ings of a series of such forms should be made so as to illustrate 

 the process of division. 



Treat with alcohol ; the green colouring substance 

 (chlorophyll) will be seen to be dissolved out of the granules, 

 but they will retain the same definite outline as before. For 

 further details as to chlorophyll see below. 



The various other bodies, which are found either having 

 definite form (such as aleurone grains), or in solution in the 

 cell-sap (such as inulin), will be described as opportunity offers, 

 later in the book : a special section at the end of the description 

 of the Angiosperms will be devoted to the study of the nutritive 

 materials stored in seeds and fruits. The reactions by which 

 the bodies commonly found as components of the plant-body 

 may be recognized, are stated concisely in Appendix B at the 

 end of the book. 



Remarks on Staining, Clearing, and Permanent Mounting. 



Staining. It is often useful to stain sections in order to 

 bring out certain points in their structure, or to distinguish 

 between bodies of nearly the same refractive index and appear- 

 ance, but of different nature. A very large number of colouring 

 matters have been used for this purpose, some of which are men- 

 tioned in Appendix A : a very few of them will suffice for 

 ordinary laboratory work, and none are ever to be used without 

 a definite purpose. 



