54 
HISTOLOGY OF VEGETABLES. 
brought to the College many years since, for the pur- 
fig. 39. pose of ascertaining its nature and the ra- 
tionale of its formation. Mr. Clift, our late 
respected Conservator, suggested that it 
might be in some way connected with the 
husks of the oat becoming mixed with 
the oatmeal, which forms a staple article 
of food among our northern countrymen ; 
hut it remained for the microscope to con- 
firm and complete the explanation, and 
Dr. Wollaston proved by the assistance of 
that instrument the identity of the elements 
of these calculi, with the hairs or setae from 
the palea of a recent oat. Two of these 
hairs are shown in Fig. 39. Similar calculi 
are sometimes formed by the accumulation of 
the hairs of the wheat husks, when brown 
bread is extensively used as an article of diet. 
The Pharus crist atus, an exotic grass, is remarkable 
for the arrangement of its silici- 
fied cells. In this grass, two 
rows or masses of silica, some- 
what resembling an hour-glass 
in shape are arranged in two 
sets ; between these, stellate mas- 
ses like raphides, are inter- 
spersed. Both forms are illus- 
Portion of the cuticle of a leaf trated in Fig. 40, but never 
of Pharus cristatus. i • • a ii 
having seen any specimen or the 
grass in its natural condition, I am unable to form a 
Hairs from 
the palea 
of an Oat. 
FIG. 40. 
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