68 
MORPHOLOGY OF THE CELL. 
b. The crystals of calcium oxalate which are imbedded in the middle lamella of 
a common cell-wall, such as those found in the soft bast of Goniferse, have evidently 
been formed in the very spot where they occur. Pfitzer has shown, on the other 
hand, that the crystals found in Citrus -vulgaris are formed in the cell-cavity, and 
become enclosed at a subsequent period by cellulose secreted from the surrounding 
protoplasm, which then coalesces in its growth, at one or more spots, with the cell- 
wall. It is highly probable that the same is the case in other instances. 
c. Cystoliths are at present known only in the Urticacese, Cannabineae, Moracese, and 
Acanthacese {Justicia, Adhatodd), In the three first-named families they occur in 
isolated but numerous cells belonging to the epidermal system, especially of the leaves, 
either in the larger epidermal cells (spe- 
cies of Ficus), which are often elongated 
from a swollen spherical base into short 
bristles (the hop, fig, Broussonetia, &c.), or 
in more deeply buried hypodermal cells 
of the upper side of the leaf, as in Ficus 
elastica (Fig. 53). In the Acanthaceae 
they occur in large numbers in isolated 
cells of the cortical parenchyma which 
are also somewhat enlarged. In all these 
cases the cystolith fills up the cell-cavity 
almost completely, no other cell-contents 
being discoverable. The mature cysto- 
lith resembles in appearance a bunch of 
grapes with its stalk, the stalk being 
attached, in Broussonetia— yN\iQx:Q^ two cys- 
toliths usually occur in a cell — to its 
side-wall. The body of the cystolith is 
hard and brittle, the stalk flexible. In a 
dark field of view between the crossed 
Nicols, I have found the cystoliths of Ficus 
elastica not luminous even in small frag- 
ments ; they do not polarise light ; the 
calcium carbonate cannot therefore be 
deposited in a crystalline form. Nothing 
of a crystalline character can be detected 
in the body itself (see Hofmeister, Lehre 
von der Pflanzenzelle, p. 180). If the 
Fig. S3.— Cystolith c <: in a hypodermal cell of Ficiis elastica; i • . • . . i -.i K K 
h h cells near the upper surface of the leaf; e. epidermis; ch the ODjCCt IS treateQ WltU aCCtlC aCIQ, DUD- 
inner tissue of the leaf containing chlorophyll. ^jgg of carbouic acld gaS arC dcVclopcd 
in the neighbourhood of the cystolith, 
while the previously opaque substance of the concretion becomes gradually trans- 
parent from without inwards. Finally, there remains behind an insignificant skeleton 
of an organic matrix, in which the calcium carbonate was evidently deposited in the 
finest state of division. No cavities are to be seen out of which crystals can have 
disappeared ; the matrix is perfectly homogeneous. Neither is there any reason for 
assuming that the lime was deposited between the layers of the matrix ; since the outer 
portion of the mass, which contains an especially large quantity of lime, is quite un- 
stratified. There is, on the other hand, a central nucleus, in direct connexion with 
the stalk, which is much denser than the external portion, and manifests an evident 
transverse stratification, as well as radiating fibres of a denser substance, which are 
obviously a faint indication of an intersecting striation. On addition of Schultz's solution 
the stratified and striated nucleus of the matrix assumes a beautiful dark blue colour, the 
outer portion only a light blue ; the former consists of denser, the latter of more watery 
