PLANT PR78I0L0GY. 



105 



by tbe 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. Make the varnish 

 by heating together equal parts of bees- 

 wax and lard. 



{g) Cotton-wood leaves have breathing- 

 pores upon both surfaces. Repeat ex- 

 periment above (/). 



(7i) Procure a well-grown geranium (20 

 to 35 cm. high) in a fiower-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 the proper place, through which to 

 introduce water. Weigh the whole at 

 intervals of a few hours. The loss will 

 be the amount of evaporation (approxi- 

 mately). By adding weighed quantities Fio. 55.— Experiment show- 



„ ii.i lii • i ing the force with which 



of water at intervals the experiment may water enters the plant. One 

 be continued indeiinitely. sixth natural size. 



(i) Cut off a rapidly growing leafy shoot of the apple or geranium 

 and place the lower end in a bottle of water. Close the bottle by 

 pressing soft wax into the mouth of the bottle around tbe stem. On 

 account of the upward movement of the water through the shoot its 

 level in the bottle will be perceptibly lowered. This will be more 

 evident the smaller the diameter of the bottle. 



{j) Make the experiment shown in Fig. 55 by fastening a leafy 

 shoot air-tight in the upper end of a glass tube ; invert and fill with 

 water, and place in a cup of mercury. The water loss by evapora- 

 tion will be replaced by water absorbed with such force as to raise 

 the mercury in the tube. 



{k) Cut off a small branch of a maple-tree on a cold winter day ; 

 bring it into a warm room. As soon as the temperature of the branch 

 rises, the sap (water) will begin to flow from the cut surface. Lower 

 the temperature and the flow will cease ; raise it again and the flow 

 will be resumed. 



(i) Cut off the stem of a rapidly growing sunflower a couple of 

 nches above the ground; slip over it the end of a tightly fitting 



