ii8 



BOTANY AND PHARMACOGNOSY. 



night when the temperature is favorable. The leaves of the 

 sundew {Drosera) are remarkable for their sensitiveness to touch. 

 The upper surface and margin are provided with peculiar hairs 

 or tentacles (Fig. yy, II) which when touched, as by an insect, 

 gradually curve inward. Not only this, the stimulus may be trans- 

 mitted to other tentacles and sometimes even the blade itself may 

 roll, inward to some extent, thus entrapping small insects which 

 serve as food to the plant. The leaves of a related plant Dionosa 



Fig. 77. So-called carnivorous plants. I, the pitcher plant (Sarracenia purpurea) 

 showing the modified pitcher-like leaves (A) with inflated portion which narrows into the 

 petiole, and a terminal, more or less spreading winged portion; and a flower and flower-bud 

 (B), II, Three species of sundew: A, Drosera rotundifolia; B, D. intermedia; C, D. 

 ongifolia. — I, after Gray; II, after Drude. 



are even more sensitive and when special hairs on the blade are 

 touched that part of the lamina bearing these hairs closes with a 

 quick, trap-like movement imprisoning its insect prey. 



Phyllotaxy, or phyllotaxis, is the study of the distribution 

 of leaves upon the stem, and of the laws which govern it. If we 

 examine germinating plants of the beech, the elm, or the oak, we 

 observe that, while the seed-leaves are opposite to each other, the 



