THE SPERMAPHYTES. 



231 



Cut longitudinal radial sections of the Milkweed stem, 

 and study the scalariform, spiral, pitted, and annular 

 vessels of the xylem, and the bast fibers and sieve tubes 

 of the phloem. Also dissect a piece of the stem that has 

 been treated with Schultze's macerating mixture, and look 

 for these vessels. 



6. Cut a transverse section of a well-developed Sun- 

 flower stem. Draw it under low power, and locate all the 

 parts you can by reference to Fig, 151, Notice that 

 the vascular tis- 

 sues are here sep- 

 arated into quite 



a number of dis- 

 tinct fibrovascu- 

 lar bundles con- 

 nected by delicate 

 interfascicular 

 cambium. Each 

 bundle develops 

 on the inner side 

 into the large and 

 small vessels of 

 the wood ; on the 

 outside, into sieve 

 tubes and bast. 



Cut longitudi- 

 nal radial sections 

 of the Sunflower stem, and study under high power the 

 scalariform, spiral, pitted, and annular vessels of the 

 xylem, and the bast fibers and sieve tubes of the phloem. 



7. Cut and study in the manner indicated in the pre- 

 ceding exercises transverse and longitudinal sections' of 

 other herbaceous Dicotyledons. Artichoke, Blackberry, 

 Raspberry, Clematis, Evening Primrose, Pigweed, and all 

 other similar stems are good. 



FIG. 151. Transverse section of the stem of Aris- 

 tolochia latifolia. A, the cambium layer ; B, the 

 xylem ; H, pith parenchyma ; E, the cortex or 

 bark; D, inner bark or phloem; C, cortical pa- 

 renchyma. 



