PLANT PHTBIOLOQY. 87 



(d) Osmosis may be demonstrated as follows: tie a piece of fresli 

 bladder securely across the mouth of a thistle-tube containing a 

 strong solution of sugar, and invert it in a vessel containing pure 

 water. The water will enter the thistle-tube, greatly increasing its 

 height, while sugar will diffuse into the water. 



(fi) Pour enough water over dry beans to cover them, put in a warm 

 place, and note the rapidity and amount of the absorption of the 

 water. 



(/) Place a quantity of fresh Pond Scum (Spirogyra) in a dish of 

 water ; expose it to the sunlight for some hours and then examine it 

 for starch with the aid of the microscope, making use of the iodine 

 test. When starch has certainly been found, put the dish in a dark 

 (but not cool) chamber, and after some hours repeat the foregoing 

 examination. No starch will now be found. 



(ji) Select two thrifty potato-plants of about equal size, and at the 

 period of flowering, when the tubers are beginning to grow, cover one 

 with a tight box or barrel, so as to shut off all the light and prevent 

 starch-making. At the expiration of a fortnight examine and com- 

 pare the tubers of the two plants . 



{Ji) Put a, dry apple-twig into a short piece of gas-pipe, closing 

 the ends, not very tightly, with clay ; put it into a fire and heat to 

 redness. The carbon left will be of the form, and about half the 

 weight of the dry twig. 



(i) Examine the roots of clover for the minute tubercles (1 mm. in 

 diameter) which have been thought to have something to do with the 

 securing of nitrogen by the plant. 



( j) Germinate a handful of Indian corn in moist clean sand, and, 

 as the plants grow, taste the kernels from time to time. The sweet 

 taste shows that the starch has changed into sugar for the nourish- 

 ment of the growing plants. 



{K) Cut off a stem of geranium and apply a bit of blue litmus-paper 

 to the moist surface. The paper will turn red on account of the 

 presence of an acid in the water of the cells. 



(Pj To show that CO2 is exhaled by plants as a result of metabolism, 

 place soaked beans in a tall cylinder, cover tightly, and keep for some 

 hours in a warm room. Upon lowering a small lighted candle into 

 the cylinder it will be extinguished by the COj. 



(m) To demonstrate that green plants exhale COj as a result of 

 metabolism, place a leafy plant under a bell-jar which fits airtight 

 upon a glass plate. With the plant put a dish containing lime-water 

 (caustic) or baryta- water. The whole is to be kept in a warm room 

 for some hours in complete darkness, when the lime or baryta water 

 will be turbid from the formation of a carbonate. 



(») Examine the vegetative filaments (organs of absorption) of 



