IMBEDDING OF CRYSTALS IN THE WALLS OF PLANT-CELLS, 289 



cellulose. In the mean time the wall of the cell in which the 

 crystal is contained (the occurrence of two within the same 

 cell being rare) undergoes thickening, and this incrustation, 

 which seems not to take place uniformly, ultimately brings 

 the cell-wall into contact with one of the angles of the con- 

 tained crystal. The deposition of cellulose still continuing 

 (fig. 2), the crystal comes, at last, in some cases to be more 

 than half buried in it ; the newest layers of the cell- wall are 

 continued over its whole surface, and the cavity of the cell 

 becomes exceedingly reduced, and finally even obliterated. 



The crystal-containing cells are found both in the leaf and 

 in the neighbourhood of the fibro-vascular bundles of the 

 stem. This latter circumstance turned Dr. Pfitzer's attention 

 to the examination of the bark of other woody plants 

 (dicotyledonous) in which Sanio had already demonstrated the 

 existence, in numerous instances of crystal-bearing cells in 

 the neighbourhood of the bast bundles. It is worth notice 

 that this is precisely their position in the monocotyledonous 

 Screw Pine. Dr. Pfitzer figures these crystal-bearing cells from 

 the bark of the root of Populus italica (fig. 4), in which tliey 

 are comparatively large, and therefore more easily examined. 

 The crystals themselves have been dissolved out by hydro- 

 chloric acid, but the cavities proper of the cells are all but 

 obliterated. Dr. Pfitzer has, however, no doubt that the 

 crystals were originally free. He finds, in fact, all stages of 

 transition between crystals which are surrounded by a thin 

 film of almost solid protoplasm and those which have a coat 

 of cellulose of every degree of thickness. 



