100 



PRACTICAL COURSE IN BOTANY 



plants of this class, with a few exceptions, like smilax and 

 asparagus, are characterized by simple, columnar stems and 

 a limited spread of leaves. Such plant forms are admirably- 

 adapted by their structure to the purposes of mechanical 

 support. It is a well-known law of mechanics that a hollow 

 cylinder is a great deal stronger than the same mass would 

 be in solid form, as may easily be tested by the simple ex- 

 periment of breaking in your fingers a cedar pencil and a 

 joint of cane or a stem of smilax of the same weight. In 

 stems that may be technically classed as solid in structure, 

 like the corn and palmetto, the interior is so light compared 

 with the hard epidermis that the result is practically a hollow 

 cylinder. 



114. Minute study of a monocotyl stem. — Place under 

 the microscope a very thin transverse section of a cornstalk. 



The little dots that looked like 

 ^ the cut ends of threads to the 



^ naked eye will now appear as 



5Px y ^^ ^p '3 



Fig. 115.— Transverse section through 

 the fibrovascular bundle of a cornstalk : 



Fig. 116. — Vertical section of the same ; 



a, annular trachcid ; sp, spiral tracheid ; a and a', rings of a decomposed annular 



ni and m', ducts ; /, air space ; v, sieve 

 tubes ; n, companion cells ; vg, strength- 

 ening fibers ; cp, bast ; /, /, parenchyma. 



trachcid ; v, sieve tubes ; s, companion 

 cells ; cp, bast ; /, air space ; vg, strength- 

 ening tissue ; sp, spiral duct. 



the complex group of cells shown in Fig. 115. The same parts 

 are shown longitudinally in Fig. 116. As seen in cross sec- 



