104 



PHYSIOLOGY OF NUTRITION. 



are surrounded by radially elongated cells arranged in a fan-like 

 manner (see Fig. 30). 



It is interesting to observe the phenomena of aggregation, which 

 under certain conditions are very strikingly exhibited in the cells 

 of the tentacles of Drosera. 2 We take a tentacle from a Drosera 

 which has always been exposed to intense illumination, so as to 



FIG. 29. Leaf of Drosera rotnndifolia, seen 

 from above. Magnified 4 times. (After Dar- 

 win.) 



FIG. 30. Tentacle, with grandnlar 

 head, of Drosera rotundifolia. Magn. 

 60. (After Strasburger.) 



favour the development of red pigments in the tentacle cells, 

 mount it in a drop of water, and examine microscopically. We 

 focus a cell of the outer layer of the tissue, and observe parietal 

 protoplasm and red sap uniformly filling the cells. We now 

 bring in contact with the secreting glandular heads of a few of 

 the tentacles of our plant very small pieces of boiled proteid. 

 After twelve to twenty hours we cut off the stimulated tentacles 

 and examine them. We see the parietal protoplasm. This now 



