98 LABORATORY EXERCISES 



b. Make a smooth cut across the young twig and the older 

 stem. If you need to saw the stem, polish the sawed surface 

 with fine sandpaper, so that you can see the markings plainly. 

 Also cut a small piece of the lilac twig lengthwise. 



Examine the cut surfaces carefully; if possible, use a mag- 

 nifier (cf. Exercise 51, c). Compare the cross section of the 

 lilac stem with Fig. 238, a, of the text. Are the two exactly 

 alike? Identify the epidermis, cortex, woody bundles, and pith. 

 Also find the pith rays and annual rings. 



c. Study a young twig and an older branch of the box 

 elder as you did the lilac. What resemblances? What differ- 

 ences? 



Do the same with one of the following: oak, poplar, cherry, 

 or elm. 



d. Examine a piece of a last year's cornstalk; it should con- 

 tain a node. Cut off the end smoothly, and examine the cross 

 section. Does the cornstalk have its materials arranged in 

 concentric circles, as the other stems have? Note that the 

 interior is pith, with woody (fibro-vascular) bundles scattered 

 through it. Draw a cross-sectional view of it. 



Cut the cornstalk lengthwise, so that you can follow the 

 course of some of the*se bundles. 



If possible, cut or saw across the handle of a palm leaf fan, or 

 of a palm leaf itself. Does the cross section resemble the corn, 

 or the lilac? 



e. Examine a potato that is sprouting, or ready to sprout. 

 Find the "eyes." What evidence is there that the scales are 

 imperfect leaves? Do the potato buds arise in the axils of the 

 leaves? How much of the potato must be planted in order 

 that a new potato plant may be formed? 



Note the color of the leaves of a potato that has sprouted 

 in the dark; why are they so? Bring the potato into bright 

 sunlight for a few hours; what change takes place? 



