ASH OF PLANTS. 27 



air. What is the effect upon transpiration of placing the flower- 

 pot in some crushed ice, the temperature of the air remaining 

 about the same as before? 



Determine the minimum, maximum, and optimum temperature 

 for transpiration of any suitable herbaceous plant, for example, 

 a Pelargonium (House Geranium). 



XL EXTRAVASATION FROM LEAVES. 



Cover a young healthy plant of Indian corn or wheat with a 

 bell-jar, being careful to keep it warm. If, after a little time, 

 a drop of water should appear at the tip of any of the leaves, 

 remove it by blotting-paper, and replace the bell-jar. What is 

 the lowest temperature at which water is thus given on" by young 

 leaves of the above plants ? 



If a young Caladium is at hand, examine the tip of the leaf 

 for the jet of water (page 268) which can sometimes be seen. 

 If the plant is a suitable one, and the jet can be seen at all, 

 ascertain the lowest temperature at which it is ejected. 



XII. INCOMBUSTIBLE MATTERS IN THE PLANT. 



Burn upon platinum foil (free access of air being permitted), 

 known weights of the following substances, and weigh the ash 

 left in each case : (1) oak-wood, (2) pine-wood, (3) a young 

 leaf of any plant, (4) a much older leaf of the same plant (for 

 instance raspberry), and (5) some grains of Indian corn. 



If no platinum foil is at hand, burn the substance in a hard 

 glass tube open at both ends and held slightly inclined in the 

 flame of an alcohol lamp or of a Bunsen burner. If the glass 

 tube is used instead of platinum foil, weigh the tube and the 

 substance together before heating, and afterwards weigh tube 

 and ash together to obtain the difference in weight. 



XIII. EXAMINATION OF THE ASH OF PLANTS. 



If the student has facilities for conducting qualitative chemical 

 analyses, he would do well to examine the ash of the following 

 plants : Sugar-beet, Buckwheat, and Oat. 



If he has had sufficient practice in quantitative chemical 

 analysis to warrant it, an examination of the ash of some one 

 of the plants which have been spoken of in 664 and 665 would 

 form a useful exercise. The investigation of the ash of a single 

 species at different seasons is recommended. 



