DR. LANKESTER, ON RAPHIDES. 947 
ing per-centage of silica im the ashes of species of Equi- 
setum :—E. limosum, 94°85, E. arveuse, 95°48, EH. hyemale, 
97°52. A complete mould in silica of the whole structure of 
these plants may be obtamed by treating them with nitric 
acid. The palms contain large quantities of silica in their 
stems. Lumps of silica, called tabersheer, are found in the 
interior of some of the palms. The ashes of Calamus ro- 
tang, according to Jablons, yielded 97:20 per cent. of silica. 
John Quekett, in his lectures on.‘ Histology,’ has given 
illustrations of the presence of silica in the glumes and 
paleze of the cereal grasses. One of the most interesting 
instances of the presence of silica amongst exogenous plants 
is that of the stellate spicules on the under surface of the 
leaves of Deutzia scabra. This very exceptional case shows 
that the appropriation of these mineral substances is no 
mere general function of plant structure, but that it is the 
result of the special organization of the plant. 
The position of raphides has been a subject of controversy. 
Raspail, who wrote on them in his usual wrong-headed way, 
asserted that they were never found in the interior of cells, 
but always in intercellular passages. Of course this was 
easily refuted, but the converse was not true, that they are 
always found in cells. The fact is, they are found in both 
positions, and even in the free surfaces and in the spiral 
vessels of plants. They have been found by Quekett loose in 
the anthers, mixed with the pollen in Hemerocallis purpurea, 
Anigozanthus floridus, and other plants. Of all the parts 
of plants in which crystals are found, the stems of herba- 
ceous plants are the most common. They are, however, founa 
in the tissues of all parts of plants. Observations are want- 
ing on the presence or absence and comparative numbers 
of these crystals at different periods of the growth of plants. 
Professor Gulliver says, that “in old, decaying, or diseased 
portions of Polygonacez, and in many other orders, crystals 
are frequent.” Observations on these would be interesting, 
as affording indications of the mineral composition of the 
living plant. 
Professor Gulliver has given an account of his observations 
on raphides, as they occurred in order. It would be of 
value to know what crystals are found in particular orders ; 
it would throw hght on the functions of plants, and explain 
some of their economy. Already we know that some plants 
grow on chalk soils, others on clay soils, whilst some again 
require phosphoric acid, and others potassium or sodium in 
excess. A minute analysis of crystals by the microscope 
may lead to a better system of manuring for cultivated plants 
