MAIZE-STEM 9 7 



tissue-forms which are transitional between sclerenchyma and 

 certain of the constituents of the bundle. 



II. Cut radial longitudinal sections of the same, treat as 

 before, and observe 



a. The epidermis, composed of oblong cells. 



b. The prosenchymatous cells of the sclerenchyma. 



c. The ground-parenchyma, with roundish cells. 



d. The vascular bundles, pursuing a longitudinal course 

 parallel to one another, without lateral fusion. 



In the xylem observe 



i. The annular, spiral, and pitted vessels, and note, especially 

 in the latter, the clearly-marked joints, pointing to their origin 

 from a succession of cells. 



ii. The pitted tracheides. 



iii. The thin-walled parenchyma. 



And in the phloem, which is easily recognized by its cellulose, 

 walls, distinguish 



iv. The sieve-tubes, which have a wide cavity, intercepted 

 here and there by transverse sieves. 



If it be found difficult to distinguish the sieve-plates, a fresh 

 section may be treated with potash ; the character of the sieve- 

 plate is then more easily seen. 



v. The cambiform cells, which are narrow and parenchy- 

 matous. 



Note the prosenchymatous constituents of the sheath of 

 sclerenchyma, and observe transitional forms between these 

 and the pitted tracheides with square ends, which belong to 

 the xylem. 



III. In order to see the fundamental arrangement of the 

 vascular system, cut median longitudinal sections through the 

 apex of a young plant of Maize, or of a foliage-branch of an old 

 plant : treat with strong potash ; or, better, with dilute potash 

 for twenty-four hours : examine with a low power, and observe, 

 if the section be median 



1. The apical cone (punctum vegetationis). 



2. Leaves, in successive stages of development, seated 

 laterally. 



3. In the older leaves, vascular bundles, which enter the stem* 



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