126 



THE PRINCIPLES OF AGRICULTURE 



flower. Fit tightly over this stub a few inches of rubber tubing, 

 partially filling the tubing with water, and into the free end fit 

 closely a small glass tube several feet long, supporting the tube 

 by a stake. In a few hours water will begin to rise in the glass 

 tube. This pressure in the common nettle may sustain a column 

 of water over ten feet in height, and in the grape-vine a column 

 more than thirty feet in height. It is inapplicable for plants that 

 force up only a small volume of water under high pressure. 



189fr. The sap ascends through the young woody parts, 

 the sap-wood in our common trees, and not between the bnrk and 

 wood, as commonly supposed. To note the special channels 



Fig. 38. Cross-section of a leaf. Stoma at a. 



Fig. 39. Four stomata. 



through which sap ascends, secure a few joints of green corn, 

 a blade of celery, a leaf of canna, and some woody branch, and 

 put the stem ends into a tumbler with a solution of some red 

 dye or stain, preferably eosin or fuchsin. Often in the course 

 of a few hours there is external evidence that the colored liquid 

 ascends through definite channels, at least with the succulent 

 herbs. Now cut off the stems and note the colored regions, 

 in the corn those thread-like groups of fibers so noticeable when 

 an old cornstalk is broken ; in the celery, likewise, through those 

 stringy fibers known to all who have eaten tough celery ; and 

 in woody plants, through the layers of wood nearest the bark. 



190o. For fuller discussions of the subjects outlined in 190 

 and 191, consult Sorauer, "Physiology of Plants for the Use of 

 Gardeners," pp. 30-44, 48-51, 



