INSECTIVOROUS AND CLIMBING PLANTS. 315 



That the glands secrete the glairy liquid of the 

 drop is evident, not only from its nature, but from its 

 persistence through a whole day's exposure to a sum- 

 mer sun, as also from its renewal after it has been re- 

 moved, dried up, or absorbed. That they absorb as 

 well as secrete, and that the whole tentacle may be 

 profoundly affected thereby, are proved by the differ- 

 ent effects, in kind and degree, which follow the appli- 

 cation of different substances. Drops of rain-water, 

 like single momentary touches of a solid body, pro- 

 duce no effect, as indeed they could be of no advan- 

 tage ; but a little carbonate of ammonia in the water, 

 or an infusion of meat, not only causes inflection, but 

 promptly manifests its action upon the contents of 

 the cells of which the tentacle is constructed. These 

 cells are sufficiently transparent to T^e viewed under 

 the microscope without dissection or other interfer- 

 ence ; and the change which takes place in the fluid 

 contents of these cells, when the gland above has been 

 acted upon, is often visible through a weak lens, or 

 sometimes even by the naked eye, although higher 

 powers are required to discern what actually takes 

 place. This change, which Mr. Darwin discovered, 

 and turns to much account in his researches, he terms 

 " aggregation of the protoplasm." When untouched 

 and quiescent, the contents appear as an homogeneous 

 purple fluid. When the gland is acted upon, minute 

 purple particles appear, suspended in the now colorless 

 or almost colorless fluid ; and this change appears first 

 in the cells next the gland, and then in those next be- 

 neath, traveling down the whole length of the tenta- 

 cle. When the action is slight, this appearance does 



