250 ELEMENTS OF BOTANY 
THE STUDY OF A SCOURING-RUSH (£QUISETUM) 
320. Occurrence. —The common horse-tail, Equisetum arvense, is 
widely distributed in the United States, east, west, north, and south. 
It is very often found on sand hills and along railroad embankments. 
The fruiting stems appear very early in the spring and are of short 
duration. The sterile vegetative growth follows, becoming well 
grown in June. ; 
321. Examination of Rootstocks and Roots. — Examine the under- 
ground portions of the plant with reference to general size, position, 
color, shape, and position of notches. After studying the stems 
above ground insert here any evident points of comparison. Do 
you find any special forms of stem development suited to a special 
purpose? Are there any organs in the nature of leaves? 
322. Sterile Stems. Examine the stems above ground with 
reference to their color and mode and degree of branching. What 
is the character of the leaves? Do the stems in any sense serve as 
leaves? Observe the nodes composing the stem and note the posi- 
tion of the leaves on the stems. Do several appear to be placed at 
the same level (whorled)? 
Examine with a magnifying glass the surface of the stem and 
note the number of ridges and grooves. Compare the number and 
position of the leaves with reference to these. 
323. Mineral Matter in Stem. — Treat small pieces of the stem 
with strong nitric acid to remove all vegetable substance and note 
the mineral substance remaining. Treat in a similar way thin cross- 
sections and examine under the microscope. The substance is silica. 
It gives the plant its gritty feeling and its name and use as “‘scouring- 
rush.” Of what use is it to the plant? Use of the same substance 
in outer rind of corn stem, bamboo stem, and straw of grains? 
324. Microscopic Examination. — Make thin cross-sections of the 
stem and examine under the lowest power of the microscope. Make 
a diagrammatic sketch to indicate the central cavity, the number 
and position of the fibro-vascular bundles, the cavity or canal in 
each, the ring of tissue surrounding the ring of bundles, and the 
larger cavities or canals outside of this. Where is the chlorophyll 
located? Can stomata be found, and if so, what is their location 
and arrangement? 
