246 DR. LANKESTER, ON RAPHIDES. 
pound crystals. They are prismatic in shape, and lie toge- 
ther in bundles of from twenty to thirty in a single cell. 
They are sometimes enveloped in a gummy matter, which, 
on being moistened, distends and bursts the cell in which 
they are contained, and the crystals escape at both ends: 
such cells have been called Biforines. E. Quekett was one of 
the first to point out that these crystals consist of phosphate 
of lime. We says, if heated red hot they do not dissolve in 
acids with effervescence—a fact which essentially distinguishes 
them from the oxalate-of-lime crystals. The acicular crys- 
tals appear to be much more abundant than any other kind. 
This fact is interesting in connection with the supply of 
phosphate of lime to the animal kingdom, and the existence 
of these acicular crystals may be made to indicate the value 
of plants which possess them, as food for man and domestic 
animals. 
Next to the oxalate and phosphate of lime in frequency 
comes carbonate of lime. It assumes a variety of forms, but 
is most frequently found in that of a pure rhombohedron. 
Crystals of carbonate of lime are often found with those of 
oxalate of lime in the Cactaceze. I have found it in every 
part of the structure and on the surface of Chara hispida. 
The next salt of lime which has been described as present 
in the tissues of plants is sulphate of lime. It is found in 
the form of double or smgle octohedrons, or in a tubular 
form, as octohedrons above and below, with the end of the 
prism obtuse. They even occur in a twin form, like the 
gypsum crystals from Montmartre. They are found, accord- 
ing to Schleiden, in Musaceze and Scitaminacee. 
Quekett refers to the presence of crystals in the fruit of 
the grape as differing from those in the leaves. These may 
be tartrate of lime. We might also expect here bitartrate of 
potass. Any of the less soluble combinations of the organic 
acids with the bases magnesia, potash, and soda, might be 
found with the aid of the microscope. 
Although silica is not usually enumerated by writers on 
raphides and crystals in plants, it must evidently be re- 
garded as one of the most important of the mineral con- 
stituents of plants. JI find nowhere any observations on 
silica in plants in the form of crystals, although Quekett, 
Schleiden, and others, speak of crystals of silica as occa- 
sionally found. The presence of silica seems essential to 
large groups of plants. As every one knows who reads the 
‘Quarterly Journal of Microscopical Science,’ the Diato- 
mace are almost entirely constructed of it. It forms the 
framework of the Equisetacez. Schleiden gives the follow- 
