ILLUSTRATIVE STUDIES 211 



is checked, as by the going down of the sun, while the absorp- 

 tive activity of the roots is as yet undiminished, they may by 

 the excretion of water prevent its filtration into the general 

 intercellular system which should be kept open for the storage 

 and circulation of the necessary oxygen and carbon dioxide. 

 Hydatodes may take on other functions in special cases, such 

 as the secretion of nectar or digestive enzymes. 



Illustrative Studies 



1. Put small segments of pine branch into a saturated aque- 

 ous solution of copper acetate, and after several weeks cut 

 sections free-hand or on a sliding microtome and study them 

 in a drop of dilute glycerine. Resin will be found stained an 

 emerald green. Study longitudinal sections in the same way 

 and draw the tubular glands from both points of view. 



2. Put a small handful of cloves into a widemouth bottle 

 and pour water over them. Stopper the bottle with a per- 

 forated cork and insert a U-tube flush wdth the lower surface 

 of the cork. Let the long arm of the U-tube extend deep into 

 another bottle. Set the bottle containing the cloves into a basin 

 of water kept boiling, and the other bottle into a basin of cold 

 water kept cold by running water or with bits of ice added 

 from time to time; this will condense the steam and oil that 

 distils over. In this way the presence of volatile oil in the 

 cloves can be demonstrated. 



3. Soften cloves in water, cut thin sections and mount them 

 in a drop of strong KOH solution. Numerous oil glands will 

 be found, and possibly needle-shaped crystals of potassium 

 caryophyllate formed by the reaction between the KOH and 

 the clove oil. 



4. Make thin sections of lemon peel hardened in 95 per 

 cent, alcohol and inclosed for sectioning in elder pith. Note 

 the globular glands in different stages of formation. How 

 close to the surface do they come? Do any of them show an 

 opening at the exterior? Draw one of the glands with the 

 surrounding tissue. 



