THE MICROSCOPE IN HISTOLOGY AND BOTANY. 133 



the amylaceous matter is dissolved. Iodine stains starch 

 blue. Starch shows in the polariscope a black cross in 

 each grain, changing to white as the prism is revolved. 



3. Chlorophyll is the green coloring matter of plants. 

 It is usually seen in the form of granules of bioplasm in 

 the interior of cells. These green granules yield their 

 chlorophyll to alcohol and ether. It seems to be neces- 

 sary to nutrition, since green plants under the stimulus 

 of light break up carbonic acid into oxygen and carbon, 

 the latter of which is absorbed. 



The red and yellow color of autumn leaves is owing to 

 the chemical metamorphosis of chlorophyll, as also is the 

 red color of many of the lower Algse, etc. In the latter 

 it seems to be in some way connected with the vital pro- 

 cesses. 



4. The coloring matter of flowers is various, and ordinarily 

 depends on the colored fluid contained in cells subjacent 

 to the epidermis, although sometimes it is in the form of 

 solid corpuscles. White patches on leaves, etc., arise from 

 absence of chlorophyll. 



5. Milky juices are true secretions contained in the lati- 

 ciferous ducts. The juice of the dandelion, caoutchouc 

 or india-rubber, which is the concrete juice of the Ficus 

 elastica, and gutta-percha, from Isonandra gutta, are exam- 

 ples. 



6. Fixed oils are found in the cells of active tissues, and 

 notably in seeds, where they serve to nourish the embryo. 

 Cocoanut, palm, castor, poppy, and linseed oils are exam- 

 ples. 



7. Volatile oil, sometimes called essential oil, is chiefly 

 found in glandular cells and hairs of the epidermis. 

 Many of them yield a resinous substance by evaporation. 



8. Camphor is analogous to volatile oil, although solid 

 at ordinary temperatures. It abounds in the Lauracese. 



9. Resin, wax, and tallow are also found in plants. The 

 bloom of the plum and grape is due to wax. 



