RELATIONS OP THE PLANT TO WATER. 25 



VI. ROOT-ABSORPTION. 

 Repeat the following experiments by Ohlert : 



Cut off the so-called spongioles, the very tips of the roots of 

 sound seedlings which have been cultivated for a few days upon 

 moist sand or sponge (or, better still, with all the roots in water), 

 and cover the wounds with asphalt-varnish. The wounded end 

 of the root must be quickly dried with blotting-paper before the 

 varnish is applied. Then put the roots of the plant again upon 

 their moist support or in water, and endeavor to answer by care- 

 ful observation the question : Does or does not the plant absorb 

 enough water for its needs without the " spongioles"? 



Cultivate seedlings of one or two plants, for instance radish 

 and wheat, upon (1) rather dry sand ; (2) moist sand ; (3) wet 

 sand, or upon blotting-paper of these three degrees of moisture, 

 and notice if there is any appreciable difference in the number of 

 root-hairs produced. Can the development of the hairs be in- 

 creased by increasing slightly the temperature of the support? 



VII. ROOT PRESSURE. 



Cut off square!}- the stem of a young dahlia or sunflower well 

 rooted in a flower-pot of moderate size, and to the stump fasten 

 immediately a T-tube, with its pressure-gauge as directed on 

 page 264. Ascertain the pressure shown by the mercurial gauge 

 at intervals of an hour, and determine also the effect of chang- 

 ing the temperature of the soil in the flower-pot. 



VIII. STEM PRESSURE. 



Apply a pressure-gauge to the cut stem of some woody plant 

 well established in a flower-pot (for instance, a strong rose), and 

 ascertain the amount of pressure exerted by the sap. 



In the winter time or early spring try the experiments referred 

 to on pages 264-267. 



IX. TRANSFER OF WATER THROUGH STEMS. 



Repeat De Vries's experiments described on page 263. For 

 these, stems of sunflower and tobacco answer very well, while 

 those of heliotrope are not very good. Ascertain the height to 

 which a color (as anilin red) will rise in the cut stern of a young 

 woody plant under different conditions of warmth, exposure of 

 the leaves to light, etc. Repeat the experiment with a strip 

 of blotting-paper, described on page 260. Try the foregoing 



