IN THE URTICACE^. 83 



the wall of the cell in which it is produced. In this case it 

 resembles, to a certain extent, a Malpighian hair developed 

 in the interior of a cell. 



The size of these cystolites is extremely variable ; those of 

 a linear or fusiform figure, nevertheless, commonly attain to 

 much larger dimensions than the others. In several species 

 of Pilea, I have observed some more than a millimetre in 

 length ; whilst, on the other hand, there are some of a sphe- 

 roidal form whose diameter scarcely reaches 2 to 3 1-lOOths 

 of a millimetre. 



I have often been able to demonstrate, and as it seems to 

 me beyond the possibility of error, the concentrically laminated 

 structure of the body of the cystolite ; but in no case have I 

 been able to perceive in the pedicle the successive layers 

 figured by Meyen and Schacht ; it has always appeared to me 

 to be a perfectly homogeneous appendage of the wall of the 

 cell, and to arise from a circumscribed and continuous thick- 

 ening of it. It behaves therefore towards reagents exactly in 

 the same way as the substance of the wall itself, except per- 

 haps that iodine develops, more frequently, traces of azotized 

 matters. This fact did not escape the notice of Payen ; and 

 it cannot be doubted that this matter has something to do with 

 the rapid development of these bodies. Perhaps the pedicle, 

 directed towards the centre of the cavity of the cell, may 

 act there like a foreign body, around which the calcareous 

 matter is deposited. However this may be, the concretion 

 and its pedicle always remain organically quite distinct. 



With respect to the physiological import of the cystolites, 

 considered generally, it is a point not easily determined with 

 precision ; but if their situation, and the time at which they 

 acquire their complete development (the fall of the leaf), and 

 lastly, their chemical composition be considered^ they would 

 appear to be rather a sort of excretion, than a secretion useful 

 in any of the functions of the plant. In this point of view, 

 therefore, the cystolites may very properly be compared with 

 other mineral matters met with in the cells of plants, and in 

 particular to those which occur in the crystalline form. Link, 

 it is true, has compared the latter to the calculi occurring in 

 animals ; but the analogy between certain of these calculi and 

 the cystolites, appears to me much more remarkable. 



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