1880. | Microscopic Crystals contained in Plants. 723 
3. Crystal prisms—These are “ acicular forms with well-marked 
faces and angles both on the shafts and tips.” They are found 
imbedded in the tissue of the plant and are never seen in bundles 
or loosely packed together, or single in a cell or intercellular 
passage. I have found as many as five of these crystals imbedded 
close together in certain tissues, but generally only one. They 
vary much in size but are generally much larger than raphides 
from which they may be easily distinguished. The family Com- 
posite furnish about the best field for the examination of this 
class of crystals, but they are much less common than the other 
forms of crystals. 
My own observations and experiments have been, at present, 
mostly confined to the natural orders Aracez, Vitacez and Com- 
posite. I examined the first two orders: especially, as they 
abounded in crystals, and this gave me a better opportunity to 
examine into their chemical composition with more sure and sat- 
isfactory results. 
In examining each specimen for the composition of the crys- 
tals, I first made the test under the microscope as far as possible, 
and in the case of inorganic crystals incinerated the substance 
and analyzed the residue. Of course from this analysis it is not 
possible to state the exact composition of the crystals, whether 
they are, for example, acid or neutral salts; but we are able to 
State with certainty what the elements are that enter into the 
crystal. And at times and under certain conditions, and also by 
analogy, the exact composition may be ascertained ; for example, 
if on examining the tissues of a plant octahedrons are found, and 
if under the microscope they do not effervesce with acetic acid, 
but do with stronger acids, and if after incineration we find on 
analysis calcium and carbonic acid, we may conclude with cer- 
tainty that these crystals are composed of calcic oxalate. How- 
ever, other acids than the one just mentioned do occur, as phos- 
Phoric and carbonic acids; the former I tested for under the 
microscope in the following manner: obtaining as large a field as 
possible of the crystals, I added a drop of hydrochloric acid and 
heated the slide slightly and then added a small amount of molyb- 
date of ammonia; heating the slide again and allowing it to — 
stand for some time, I placed it under the microscope, when, if 
any phosphoric acid was present the characteristic crystals of 
phospho-molybdate of ammonia would appear. These crystals 
