146 VITALITY IN POLLEN TUBES, ORCHIDS, [BOOK n. 



In like manner the pollen tubes of the grains enclosed in 

 the pollen masses of Asclepiads are uniformly directed towards 

 a thin place in the side of the bag which encloses them, and 

 having pierced that place,, proceed invariably to the part of 

 the style or stigma destined to receive them, in Morrenia 

 overcoming great obstacles in doing so. In Armeria a plug 

 passes down from the dome of the ovary and unerringly closes 

 up the foramen of the ovule at the time of impregnation. In 

 other plants the pollen tubes themselves are introduced into the 

 foramina of the ovules with as much exactness as if they were 

 capable of seeing where they had to pass. Such facts are 

 inexplicable upon any known mechanical principle. 



If any one of six bristles planted perpendicularly upon the 

 leaf of Dionsea muscipula is irritated, the sides of the leaf 

 collapse, so as to cross the cilise of their margin, like the teeth 

 of a steel-trap for catching animals. And it is only by touch- 

 ing the bristles that the effect is produced. Roth is recorded 

 to have seen something of the same kind in Drosera rotundi- 

 folia. If the bottom of the stamens of the common berberry 

 is touched on the inside with the point of a needle, they 

 spring up against the pistil. The column of the genus Styli- 

 dium, which in its quiescent position is bent over one side of 

 the corolla, if slightly irritated, instantly springs with a jerk 

 over to the opposite side of the flower. In Megaclinium 

 falcatum, the labellum, which is connected very slightly with 

 the column, is almost continually in motion ; in some species 

 of Pterostylis is observed a kind of convulsive action of the 

 labellum. In the Appendix to the Botanical Register two 

 Orchids are figured in which some most curious phenomena 

 are observable. In the one the labellum, which is hammer- 

 headed and placed on a long arm with a moveable elbow 

 joint in the middle, is said to resemble an insect suspended in 

 the air and moving with every breeze. Another singular case 

 of spontaneous motion is that of Hedysarum gyrans. This 

 plant has ternate leaves : the terminal leaflet, which is larger 

 than those at the side, does not move, except to sleep ; but 

 the lateral ones, especially in warm weather, are in continual 

 motion, both day and night, even when the terminal leaflet 

 is asleep. External stimuli produce no effect ; the motions 



