Exercise XV 



ORGANIZATION OF HIGHER PLANTS 77 



Planf 



Funnel 



Open capillary 

 with scale 



A=»4;« 



tion (called a potometer) should be set up as 

 shown in the diagram. Keep the stem of the cut 

 plant in water until the rest of the setup is ready 

 to receive it. Wire all joints for a tight fit. 



Before attaching the plant, be sure all other 

 joints are tight, and fill the entire apparatus with 

 water. Shut off" the funnel, which serves as a 

 water reservoir, from the rest of the apparatus 

 with the pinchcock. 



When the potometer is ready, slice off" the 

 bottom one-fourth to one-half inch of the stem 

 Vyhile it is still under water; then quickly push it 

 into the open end of the rubber tubing which is 

 filled with water. Be sure no bubble of air is 

 caught in the joint. Use the tubing stretchers to 

 aid in inserting the plant; then coat the outside of 

 the joint with a little vaseline. (Be sure not to get 

 vaseline on the cut surface!) Clamp the plant so 

 that the cut end is at about the same level as the 

 top of the capillary. Add water if needed to the 

 funnel, so that its level is higher than the top of 

 the capillary. Then open the pinchcock so as to 

 fill the capillary with water, and tightly close it 

 again. 



As water is lost from the leaves by transpira- 

 tion, the water level in the capillary drops. Let 

 this go on for a convenient interval, and note the 



time and change of water level. By reopening the 

 pinchcock, bring the water level in the capillary 

 back to near the starting point, and repeat the 

 measurement. 



After a few consecutive readings are in good 

 agreement with one another, calculate the rate 

 of transpiration, per hour, day, and year. Direct 

 a light on the geranium plant; does the rate of 

 transpiration increase? What is the eff"ect of a 

 stream of air blowing on the leaves ? 



PLANT STRUCTURE 



We have already noted that the tissues of 

 higher plants, like those of higher animals, can 

 be divided into four types. Meristematic tissue 

 is responsible for the production of new cells, 

 and the growth of the plant. The new cells 

 formed from the meristems may diff"erentiate 

 into any one of the other three types of plant 

 tissue. The protective tissues (epidermis and 

 cork) comprise the outermost layers of the plant. 

 The "fundamental" tissues are more variable in 

 function and type. Some of them provide sup- 

 port (fiber tissue : sclerenchyma and collenchyma); 

 others are concerned with photosynthesis (paren- 

 chyma). There are two kinds of conductive 



