FUNCTIONS OF LEAVES 163 



Group III. Live-for-ever (Sedum Telepkium), Bryophyllum, English 

 ivy, " ivy-leafed geranium," (Pelargonium peltatum), or any of the 

 fleshy-leafed begonias. 



Group IV. Hydrangea (//. Hortensia), squash or cucumber, sun- 

 flower. 



The plants should be growing in pots and well rooted. Water 

 them well and then put them all in a warm, sunny place. Note the 

 appearance of all the plants at the end of twenty-four hours. If any 

 are wilting badly, water them. Keep on with the experiment, in no 

 case watering any plant or set of plants until it has wilted a good 

 deal. Record the observations in such a way as to show just how 

 long a time it took each plant to begin to wilt from the time when 

 the experiment began. If any hold out more than a month, they 

 may afterwards be examined at intervals of a week, to save the time 

 required for daily observations. If possible, account by the struc- 

 ture of the plants for some of the differences observed. Try to learn 

 the native country of each plant used and the soil or exposure natural 

 to it. 



173. Course traversed by Water through the Leaf. The 

 same plan that was adopted to trace the course of water in 

 the stem (Exp. XXI) may be followed to discover its path 

 through the leaf. 



EXPERIMENT XXXIII 



Rise of Sap in Leaves. Put the freshly cut ends of the petioles 

 of several thin leaves of different kinds into small glasses, each con- 

 taining eosin solution to the depth of one-quarter inch or more. 

 Allow them to stand for half an hour, and examine them by holding 

 up to the light and looking through them to see into what parts the 

 eosin solution has risen. Allow some of the leaves to remain as 

 much as twelve hours, and examine them again. The red-stained 

 portions of the leaf mark the lines along which, under natural con- 

 ditions, sap rises into it. Cut across (near the petiole or midrib 

 ends) all the principal veins of some kind of large, thin leaf. Then 

 cut off the petiole and at once stand the cut end, to which the blade 



