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O. F. BLACK 
has, nevertheless, been a distinct prejudice against the plant which has 
acted adversely to its extended use, due to the intensely acrid taste of 
the raw leaves and to a less degree of the tubers. Both portions of 
tlfe plant were known to possess the raphide-filled cells, and this has 
been assumed to be the cause of their acridity. There were, however, 
certain reasons for suspecting that this was not entirely the case, and 
as the plant is one of considerable food value it seemed advisable to 
make a study of it in this respect. 
The evidence that raphides are calcium oxalate and not calcium 
citrate is very complete, although some confusion has existed on this 
point, as the two salts have many properties in common. By careful 
analytical work F. G. KohU has shown beyond reasonable doubt that 
raphides are the oxalate, and quite recently H. Ziegenspeck,^ who seems 
to be unfamiliar with Kohl's research, has prepared from raphides pure 
oxalic acid which he identified by its characteristic physical properties, 
thus furnishing absolutely conclusive proof of the composition of the 
crystals. 
On the question of the cause of the acrid taste of raphide-containing 
plants the evidence is less direct. Much has been written about such 
plants, the general opinion seeming to be that the raphides serve as a 
protection to the plants against animals and insects, although one 
writer, A. Schneider,^ takes the ground that such is not the case, but, 
on the contrary, that calcium oxalate crystals serve the plants as a 
tissue support and add to their structural rigidity. E. Stahl'^ studied 
the effect of a variety of raphide-bearing plants when fed to hungry 
snails and reached the conclusion that the burning taste depends on the 
raphides alone, but his conclusion is arrived at through a process of 
reasoning rather than by experiment. The experiment of Barnes^ has 
a more direct bearing on the question. He macerated a raphide-bear- 
ing plant in water and then subjected it to filtration through such a fine 
filtering medium that no raphides could pass. The resulting filtrate 
showed no sign of acridity, and hence he concluded that the raphides 
were solely responsible by mechanically irritating the mouth. As 
raphides were not the only material removed by the filtration, his 
conclusion was rather more sweeping than the experiment warranted. 
1 Anatomisch-physiologische Untersuchungen der Kalksalze und der Kieselsaure 
in der Pflanze. p. 91. Marburg, 1889. 
2 Ber. Deutsch. Bot. Ges. 32: 630-633, 191 5. 
3 Bot. Gaz. 32: 142-144. 1901. 
^ Pflanzen und Schnecken. Jena, 1886. 
^Barnes, C. R. Bot. Gaz. 13: 232-233. 1888. 
