144 Transactions of the Royal Microscopical Society. 
and occurring loosely together in bundles of about a score or more, 
commonly within a cell. 
2. Sphser aphides. — Globated forms made up of minute crystals 
or granules, and either smoothish, granular, or still rougher from 
projecting crystalline tips, and generally within a distinct cell ; the 
cells often forming a tissue, like mosaic work. 
3. Long Crystal Prisms. — Acicular forms with angular shafts 
and tips, never occurring loosely in bundles, but either singly or 
two or more fused together and firmly seated in the plant-tissue. 
4. Short Prismatic Crystals. — Cubical, long and short squares, 
polyhedrons, rhombs, and many forms defying definition, though 
generally more or less prismatic, often not at all so, and occasionally 
mere crystalline granules ; occurring mostly in distinct cells, fre- 
quently arranged in chains along the vascular bundles of the leaves 
and other parts of the plant, or spread in a tissue in the testa. 
More ample descriptions are given in my former memoirs. In 
searching for the crystals, a fragment of the plant should be mashed 
to a pulp by the point of a penknife in a drop of water on the 
object-plate, then pressed by a thin cover of glass, and examined 
under an objective of half-an-inch or deeper focus ; and if the part 
of the plant be first boiled for a few minutes in a solution of caustic 
potass, the distinctness of the crystals and their cells will be much 
improved. Thus there can be no difficulty in finding and discri- 
minating the different crystals to which the list is a guide. 
It must, however, be borne in mind that several forms may 
occur either together or in diverse parts in the same plant. To 
cite a few examples : while raphides are so abundant in the leaves 
and other parts of Tamus, very fine short prismatic crystals are 
present in the testa ; in Geraniacese the sepals contain sphaeraphides, 
and the pericarps the short prismatic crystals ; in Thelygonum and 
some Liliaceae raphides and long crystal prisms occur together ; in 
Vitaceae raphides and sphaeraphides, and so too in Melanthaceae ; 
in Aceraceae the leaves have sphaeraphides and the short prismatic 
crystals, while the testa has only the last forms ; which, too, are 
remarkable in the testa of Ulmaceae, while sphaeraphides are con- 
tained in the leaves of this order ; in several Mesembryaceae 
raphides abound, an,d therewith occur other forms, acicular, flat- 
tened, and irregularly angular ; in some Commelynaceae and Brorne- 
liaceae three or all the four forms of crystals appear together in the 
leaves and stems. It is further noteworthy that, while iik the fruit 
of one Composite plant, as Serratula tinctoria or Centaurea nigra, 
the long prisms occur, in the same part of some allied plants, as 
Centaurea scabiosa and Arctium intermedium, the short crystals 
only are found ; and this curious specific difference appeared con- 
stantly in several specimens from different localities. 
In the following list the systematic names are taken from the 
