Hooker: Movement in Drosera rotundifolia 



393 



2. During rapid bending the osmotic concentration of the 

 abaxial cells in the growing region decreases. 



3. When the tentacles are bent, the cells have a higher osmotic 

 concentration than at any other time. 



2. Rabdoids 



Rabdoids were first discovered by Gardiner ('85) in Drosera 

 dicJwtoma, and he states that in Dionaea, Drosera rotundifolia and 

 other species of Drosera rabdoids occur which resemble those of 

 Drosera dichotoma. Gardiner described the rabdoid as a body, 

 usually spindle-shaped or acicular, which occupies such a position 

 that it stretches diagonally across the cell from end to end, the 

 two extremities being imbedded in the cell protoplasm. They 

 were present in all the epidermal cells of Drosera dicJwtoma leaves 

 except the gland cells and the cells immediately beneath the glands. 

 In the bending region of those tentacles capable of movement 

 they were larger in the epidermal cells on the abaxial side than on 

 the adaxial side where they were very small or apparently absent. 

 When these cells lost their turgidity the rabdoids contracted and 

 separated into two or more parts, but regained their spindle shape 

 when turgidity was restored. A sudden blow on the cover glass 

 also caused the rabdoids to assume a spherical form. 



The presence of rabdoids in the epidermal cells of Drosera 

 rotundifolia leaves was confirmed. They occur in all the epidermal 

 cells of the petiole, of the leaf blade and of the basal portion of the 

 tentacles, including the bending region. Each cell contains a 

 single rabdoid, rarely two rabdoids, situated near the outer wall 

 and parallel with it. After a leaf has fed on insects, the rabdoids 

 are distinctly larger than before. When plants are deprived of 

 insectivorous food for any considerable period, the rabdoids 

 dwindle until they are barely noticeable. Sudden shocks produced 

 by tapping the cover glass or gradual pressure sustained for a 

 considerable period of time cause the rabdoids to alter their shape. 



