146 Transactions of the Royal Microscopical Society. 
diagnostic than any other single one afforded by these plants ; 
fundamental, because it appears from the beginning, sometimes in 
the ovule, and regularly in the seed-leaves and plumule ; universal, 
because thereafter the raphides pervade the plant generally, at all 
times, in mere fragments of the species, and even after its decay. 
Thus, for example, a plant of one of these three orders may, at any 
period of its growth, or even in rotten portions, be surely known 
from the species of the allied orders. Accordingly, Onagraceae may 
he truly and sharply defined thus — Calycifloral Exogens in which 
raphides abound ; and so in like manner of the orders Balsaminaceae 
and Eubiaceae. Though no exceptions to this rule have yet been 
found in the British flora, it would be rash to assert that none 
exist ; for even some of the best botanical definitions in universal 
use are by no means unexceptional. And as to the flora of the 
world, far more investigations are necessary to determine the taxo- 
nomic value of the crystals ; hut we already know they may in 
many respects afford useful diagnostics in practical pharmacy and 
gardening. In floriculture, using this character, I have been able 
to extricate accidental confusion among young thick-leaved things, 
truly selecting the Mesembryaceae from the Crassulaceae, and to 
distinguish other plants before they had grown above ground in 
the reserve beds of the garden. Thus we have before us another 
pleasing and instructive employment for the microscope in rural 
economy. In pharmacology this kind of diagnosis has long been 
known ; and it is ready for useful service, though not yet enlisted, 
in the British flora. 
II. Sphseraphides . — These are more frequent in Exogens than 
raphides, and are common too in Endogens. The distribution of 
sphseraphides has not yet been well determined in the British flora, 
and in the flora of the world has been still less accomplished. 
III. Long Crystal Prisms are much less frequent than the three 
other forms, and in British plants are by no means common. In 
the Composite of the above list these prisms are comparatively 
small ; they occur in the fruit, and may he best seen in the ovary 
while it is yet soft, and seldom or never elsewhere in the plant. 
The exotic examples mentioned in the list are all excellent, larger, 
and easily procurable. 
IY. Short Prismatic Crystals are widely diffused and abundant. 
In the Compositae they are, like the long prisms, confined chiefly to 
the pericarp ; and in Leguminosae form beautiful chains along the 
vascular bundles, which may be conveniently examined in the 
leaflets of the common white or Dutch clover, and in the young 
pods of most species of the order. 
Canterbury, July 24 , 1877 . 
