APPENDIX. 
555 
combination with silver of phosphoric acid, which must have been 
furnished by the acicular Raphides. 
“ Though phosphoric and oxalic acids united with lime are found 
the most frequent components of these minute crystals, there can 
be no doubt that tartaric acid enters into their formation in 
certain plants, as in the fruit of the Grape, where the crystals are 
found of a different figure from those in the interior of the leaves or 
stem ; and also that magnesia can be frequently detected combined 
wdth lime, and perhaps never forms crystals with acid, without 
lime entering also into their composition. 
Silica, though it frequently forms an organised part of vegetables, 
seldom exists as crystals in their interior. In a bark from Para, 
which is said to be manufactured into a kind of pottery, silica 
exists in abundance in granular fragments, which, however, do not 
put on a crystalline form. 
“ Conclusion . — It is not known what purposes these bodies fulfil 
in the economy of plants, but it has been conjectured, since amy- 
laceous matters are deposited, and again appropriated for the 
support of the carbonaceous portion of the tissue, according to the 
necessities of the individual, that these crystals may be deposits 
to be applied towards the mineral part or skeleton of the plant, as 
occasion may require : but it has been found from experiments 
that these calcareous bodies are insoluble in vegetable acids, and 
the silica of course in every thing ; consequently they cannot be 
taken up again, are therefore unsuited to the vital exigencies of the 
vegetable, and probably are of no use, even mechanically, in the 
several tissues which contain them, because plants of many kinds 
do not secrete such formations : therefore, it will be nearer the 
truth to regard them, as Link has done, as nothing more than 
accidental deposits. 
In all the analyses lime has been found the greatest constituent 
of these bodies : and since this material is so intimately associated 
both with animal and vegetable organisation, as not perhaps to 
be wanting in any individual of either kingdom, there is every 
reason for its being so generally the base of such crystals. More- 
over, since it is the property of some vegetables to combine, out 
^ of their materials of sustenance, varied proportions of oxygen and 
carbon, which, when apportioned in the ratio of three of the former 
to two of the latter, form oxalic acid, the presence of that agent 
in a plant, in contact with lime, can scarcely fail in producing 
a crystalline substance with it. Again, as phosphoric acid is a 
frequent accompaniment of animal and vegetable organisation either 
