62 Plant Physiology 



Root-cap. Make a preparation of the whole root-tip of 

 barley and note with the low-power of the microscope the 

 general extent of the root-cap, the histology of which may only 

 be studied by adequate sections. 



Root- dp. Make longitudinal sections of the root-tip of corn 

 or sunflower and compare with those of pea or vetch, distinguish- 

 ing and describing primordial meristem, central cylinder, ple- 

 rome, epidermis, and root-cap. Hand sections are sufficient, 

 if properly made, but prepared slides are also desirable. 



Unavailable water. Use young plants of cucumber, lettuce, 

 and barley or wheat grown under similar conditions in small 

 pots of rich or heavy loam and pure sand or quartz [preferably 

 those soils the water-content of which were determined earlier]. 

 The pots should contain no moss or such material at the 

 bottom. When wanted for the experiment, the plants should 

 be barely supplied with adequate water, so that during the 

 laboratory period incipient wilting may begin. At the moment 

 of wilting of each plant weigh out a portion of the soil of the 

 pot and record the weight. These samples are retained and 

 subsequently dried to determine the content of unavailable 

 water in the different types. 



Water absorbed by leaves. Secure leaves of lettuce, peach, 



good aeration. Seed grown for physiological purposes should not be 

 turned over or shaken during germination, as curvature of the roots is 

 likely to result. In testing seeds for vitality, where numerous varietiea 

 or sorts are employed, special boxes with ruled spaces, each space de- 

 signed for a given number of seed, are important. Information regard- 

 ing this matter may be obtained from any bulletin on seed-testing. 



In the laboratory it is often desirable to obtain root-hairs in full 

 development; in such cases flower-pots or special porous germinators 

 (covered saucers) may be employed. With small seed, such as lettuce, 

 mustard, etc., the procedure may be as follows: moisten the germinator 

 or pot and sling a few seed against the inner surfaces. They will adhere 

 to the surface at convenient distances apart, and then if provided with 

 sufficient moisture, absorbed through the walls of the vessel, a rapid and 

 vigorous germination will result, and the development of root-hairs will 

 be shown in a simple and striking manner. 



