578 
POPULAR SCIENCE REVIEW. 
the tissue in which they are seated ; and when the cell can be 
seen_, it is closely investing the crystal. Of the four-sided 
prisms_, the faces may either be all equal_, or two of them 
broader than the other two ; and of the three-sided prisms, a 
transverse section of the shaft may be either an isosceles or 
equilateral triangle. A longitudinal cleavage through the 
centre of two opposite faces of the equally four-sided prism 
would form that with two sides broader than the other two; 
and a longitudinal cleavage, diagonally from angle to angle, of 
these two square shafts would give the equilateral and isosceles 
triangles. Crystal prisms are commonly larger, sometimes 
smaller, than raphides, and vary in size in the same plant, and 
still more in different orders : in the root- stock of Florentine 
Iris they have an average length of and thickness of 
of an inch ; in the leaves of Iris jmmila smd Gladiolus insignis, 
L. of and T. of -g^o of an inch ; in the middle layer 
of the testa of Silybum, l. -5^, t. the ovary- 
coat of CarduuSj L. t. - 4 -- A 0 j ttie same part of 
Centaurea nigyri, L. two-oj t. j the bark of Quillaja, 
1^0) T. ^6^0 0 j ill the bulb-scales of Allium, l. T- ef 
an inch. Dr. Davy found them in the Iris composed 
oxalate of lime; in Allium, of oxalate of lime and mag- 
nesia. 
Spheeraphides are more or less rounded bodies, often spherical, 
chiefly made up of crystals or crystalline matter, commonly 
opaque and whitish, unless where the ends of the crystals 
project at the circumference and appear transparent. These 
ends often give a stellated appearance to the sphaeraphides, 
which are as frequently with the projecting points much shorter, 
and as frequently merely rough or granular on the surface. The 
jutting tips are many times sharp ends of prisms, and portions 
of the prismatic shafts may be often seen broken out of the 
sphaeraphides, by pressure, on the object-plate of the micro- 
scope. Sphaeraphides vary much in size in the same plant, and 
still more in different orders ; — in Chenoj)odiacece, Sesuviacece, 
Scdoragaxeoe, the shrubby Cinchonacece, and many other orders, 
commonly about yIo 0 of an inch in diameter ; T2V0 of an 
inch in Pistia, and very much larger in some Cactacece. They 
are smaller than their cells, and often occur so regularly 
therein, so studded throughout the cellular network, as to 
make part of a beautiful structure. This I have depicted, under 
the name of sphseraphid tissue, from Lythrum,* which includes 
the similar forms long before described by Quekett in the Elm 
and Cranesbill. He called them conglomerate raphides ; but 
* Annals of Natural History, September, 1863. 
