FUNCTIONS OF LEAVES | 163 
Group III. Live-for-ever (Sedum Telephium), Bryophyllum, English 
ivy, “ivy-leafed geranium,” (Pelargonium peltatum), or any of the 
fleshy-leafed begonias. 
Group IV. Hydrangea (H. 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. X XI) may be followed to discover its path 
through the leaf. 
EXPERIMENT XXXII 
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 
