68 



MORPHOLOGF 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 Goniferae, 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 Urticaceae, Cannabineae, Moraceae, and 

 Acanthaceae {Justiciar Adhatoda). 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— where 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 

 object is treated with acetic acid, bub- 

 bles of carbonic acid gas are developed 

 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 



Fig. S3.— Cystolith c c in a hypodermal cell of Ficus elastica ; 

 h h cells near the upper surface of the leaf; e epidermis ; ch the 

 inner tissue of the leaf containing chlorophyll. 



