II. THE LEAF: ITS USES 



TRANSPIRATION 



Material. — Freshly cut sprigs of various Itinds, bearing healthy 

 leaves ; a leaf of the white garden lily (Z. candiduiti) or of the wander- 

 ing Jew {Zebrina pendula) ; two hermetically sealing preserve jars ; a 

 little beeswax or tin foil ; a bit of looking glass ; a number of empty 

 bottles with perforated stoppers or rubber cloth covers. 



Note. — In order to avoid cumbering the pages of the text with tech- 

 nical nomenclature, botanical names of specimens mentioned will be 

 given only : First, in the case of foreign or little known species ; 

 Second, where the popular name is local or provincial, or where the 

 same term is applied to several different plants ; and Third, where 

 special accuracy of designation is required. 



14. Why Leaves wither. — Dry two self -sealing jars 

 thoroughly, by holding them over a stove or a lighted lamp 

 for a short time to prevent their " sweating." Place in one 

 a freshly cut leafy sprig of any kind, leaving the other 

 empty. Seal both jars and set them in the shade. Place 

 beside them, but without covering of any kind, a twig simi- 

 lar to the one in the jar. Both twigs should have been 

 cut at the same time, and their cut ends covered with wax 

 or vaseline, to prevent access of air. At the end of six 

 or eight hours look to see if there is any moisture de- 

 posited on the inside of either jar. If there is none, set 

 them both in a refrigerator or other cool place, for half 

 an hour, and then examine them again. On which jar is 

 there a greater deposit of dew ? . How do you account for 

 it.? Take the twig out of the jar and compare its leaves 

 with those of the one left outside; which have withered 

 most, and why .' 



15. Transpiration. — We learn from experiments like 

 the foregoing that one office of leaves is transpiration, or 



IS 



