THE CELL. 



23 



(blue and violet). Some of the Schizomycetes (Beggiatoa) secrete 

 sulphur within the cells. Some algae (Desmidiacece) secrete 

 gypsum (OaS0 4 +2H,0). 



Calcium oxalate crystals are plentifully distributed in the cells 

 of the entire vegetable kingdom. In most instances this lime-salt 

 remains unchanged wherever formed. Yery generally these crystals 

 appear in the form of clusters (Drusen) ; frequently they occur as 

 acicular bundles called raphides, less frequently as perfect crystals. 

 STAHL studied these crystals, especially the raphides, in regard 

 to their function, and decided that they served as a protection to 

 the plants against destruction by snails and grasshoppers. (Feeding 

 experiments.) Fig. 9 shows raphides; Fig. 10, perfect, well-de- 

 veloped crystals. 



FIG. 9. Cells from the stem of Trades- FIG. 10. Crystal-bearing cells of Aesculus 

 cantiazebrina. (After Haberlandt.) Hippocastcmum. (After Haberlandt.) 



The first more exact studies of these crystals were made by 

 HoLZNER. 1 The perfect crystals belong either to the tetragonal or 

 the clinorhombic system, as do also the artificially produced crystals, 

 this depending upon whether they contain one or three molecules 

 of water of crystallization. The clusters are aggregates of usually 

 not very small crystal individuals around a nucleus of protein 



1 Flora, 1864. 



