62 
HISTOLOGY OF VEGETABLES. 
Tliin section of Pear , show- 
ing a mass of gritty tissue 
amongst the cells. 
fig. 45 . 
and consists of a number of cells 
aggregated together in small 
bundles, somewhat in the shape 
of a star, or a mass of conglo- 
merate raphides. When a thin 
section of Pear is examined with 
a power of ninety diameters, as 
shown in Fig. 44, these stellate 
masses are readily seen amongst 
the cellular tissue ; but when a 
higher power is employed, as of two hundred and fifty 
diameters, and the cells have been slightly separated 
from each other by maceration 
or boiling (Fig. 45), each ex- 
hibits a distinct central cavity 
with tubes radiating from it, 
and the solid deposit contained 
within the cell, is almost as clear 
and transparent as quartz, and 
refracts light very strongly. 
This is the sclerogen of Tur- 
pin, and it is the same mate- 
rial that gives hardness to the stone of the Plum , 
Apricot , Peach , &c., to the shell of the Cocoa and 
Coquilla nut , and which is so dense and white in the 
fruit of a Palm , Phytelephas macrocarpa , as to have 
obtained the name of vegetable ivory. 
Some of these structures are so hard as to be em- 
ployed in the arts for various purposes ; the albumen 
Isolated cells from the scle- 
rogenous, or gritty tissue of 
the Pear. 
