76 BOTANY. 
stream in another, does not exist. Likewise, the belief still main- 
tained by some people that in the autumn or early winter ‘‘the sap 
goes down into the roots,” and that ‘‘it rises” in the spring, is en- 
tirely erroneous. There is actually more water (sap) in an ordinary 
deciduous tree in the winter than there is in the spring or summer 
“(excluding of course the new and very watery growths). 
Practical Studies.—A few physiological experiments may be casily 
made by the student. ‘The following will serve as a beginning: 
(a) Collect a quantity of green grass in the middle of the day when 
it is not wet; weigh it accurately, then thoroughly dry it in an oven, 
being careful not to scorch it. Weigh again: the difference in the. 
two weighings will be approximately the amount of water in the 
living plant, although some water will still be left in the plant by 
ordinary drying. 
(0) Weigh a handful of beans; put them into warm water or moist 
earth for a day or two until they are beginning to sprout. Then 
gather them up carefully, wipe off all external dirt and moisture, and 
weigh again. Here the difference will be approximately the amount 
of water absorbed by the protoplasm. 
(c) Place some specimens of Green Slime or Pond Scum on a dry 
glass slip, using no cover-glass. Note with the microscope the rapid 
evaporation of water as shown by the collapsing of the cells. 
(d) Gather fresh leaves of clover; suspend some of them under a 
bell-jar or inverted tumbler which stands in a plate containing a little 
water. Put the other leaves into a dry plate with no protection from 
the dry air. Note that the evaporation is very much more rapid in 
the dry air than in the moist air under the bell-jar. 
(e) Strip off the epidermis from a leaf (hyacinth, live-for-ever, etc., 
are good) and note that the evaporation is much greater (as shown 
by the more rapid wilting) than from the uninjured leaf. This shows 
that the epidermis and its breathing-pores retard evaporation. 
(f) Lilac-leaves have breathing-pores upon their lower surfaces 
alone. Provide two leaves: cover the lower surface of one with a 
thin coat of varnish, which will prevent evaporation through the 
breathing-pores; suspend both in a current of dry air, and note that 
the one not varnished withers sooner than the other. 
(g) Cottonwood-leaves have breathing-pores upon both surfaces, 
Repeat experiment above (/). 
(2) Procure a well-grown geranium (20 to 25 cm. high) in a flower- 
pot. Cover the pot with a piece of thin sheet-rubber, tying it care- 
fully around the stem of the plant. Insert a short tube (provided 
with a cork) at the proper place, through which to introduce water. 
