THE AMERICAN BOTANIST 121 



leaf pulp out of them. At this point the veins may be bleach- 

 ed with a bleaching powder or colored with various aniline 

 dyes. After the veins have been cleared of pulp they may be 

 dried between blotters and then mounted either by placing be- 

 tween two sheets of glass and binding with passepartout paper 

 or by mounting on a sheet of contrasting cardboard and cover- 

 ing with glass. Those mounted between two sheets of glass 

 may be used with the stereopticon. 



Metabolic Water. — The starches cellulose and sugars of 

 plants belong to a class of foods known as carbohydrates be- 

 cause they consist of carbon hydrogen and oxygen. Such 

 foods are formed by the union of carbon derived from the 

 carbon-dioxide in the air with soil water taken up by the roots. 

 When they are oxidized as in the process of respiration oc- 

 curring in both animals and plants, the carbon is again set free 

 in carbon-dioxide and the water remains in the organism. 

 This water is called metabolic water. The addition of water 

 to the plant in this way, or in dehydration, as when water is 

 withdrawn from one substance in changing it to another, is 

 now regarded as being of much more importance than is com- 

 monly supposed. The complete oxidation of starch or cellu- 

 lose leaves more than half the original weight of water while 

 the dehydration of glucose when changed to starch sets free 

 ten percent of water. The existence of metabolic water ex- 

 plains how the clothes moth and bean weevil which never have 

 a chance to get a drink are, nevertheless, fat and juicy. Their 

 moisture comes from the oxidizing of the substances upon 

 which they feed. 



