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 
ile hud ett 
Ta 
al 
SEMEN ANSE 
Fia. 115.—Transverse section through : ne 
the fibrovascular bundle of a cornstalk: Fic. 116. — Vertical section of the same ; 
a, annular tracheid ; sp, spiral tracheid; @ and a’, rings of 4 decomposed annular 
m and m’, ducts; J, air space; v, sieve tracheid; v, sieve tubes; s, companion 
tubes ; s, companion cells; vg, strength- cells; cp, bast; 1, air space; vg, strength- 
ening fibers ; cp, bast; f, f, parenchyma. 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- 
