76 BOTANY. 



stream in another, does not exist. Liliewise, the belief still main- 

 tained by some people that in the autumn or early winter " tlie 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 llian tliere is in the spring or summer 

 (excluding of course the new and very watery growths). 



Practical Studies. — A few physiological experiments may be easily 

 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 diflferenoe 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. 



(6) "Weigh a handful of beans; put them into warm water or moist 

 earth for a day or two until tliey 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 tlie evaporation is much greater (as shown 

 by the more rapid wilting) than from the uninjured leaf. This shows 

 that the epidermis and its breatliing-pores retard evaporation. 



(/) 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 varuishea withers sooner than the other. Make the var- 

 nish by heating together equal parts of beeswax and lard. 



(p) Cottonwood-leaves have breathing-pores upon both surfaces. 

 Repeat experiment above (/). 



(70 Procure a well-grown geranium (30 to 35 cm. high) in a flower- 

 pot. Cover the pot with a piece of thin sheet-rubber, tying it around 

 the stem of the plant. Insert a short tube (provided with a cork) at 



