536 LECTURE XX. 



somewhat on their own axes so that the figure described by 

 the apex is an irregular oval or ellipse. The rapidity of the 

 movement varies with the temperature ; but at a moderately 

 high temperature (30 40 C.) the cycle is completed in about 

 two minutes. In Averrhoa bilimbi (Lynch) the spontaneous 

 movements of the leaflets are very striking. Some instances 

 of spontaneous movement of floral organs are also known, 

 and although it has not been definitely ascertained whether 

 they belong to the category of movements of variation ; or 

 whether they are due to growth, like the opening and closing 

 of flowers (pp. 378 400), it seems probable that the former 

 is the case. A well-marked case is that of the labellum of 

 Megaclinium falcatum^n African Orchid, described by Morren : 

 the labellum consists of a limb and a claw, and the former 

 oscillates upwards and downwards on the latter. Another, 

 again, is the movement of the gynostemium of Stylidium 

 adnatum. From the researches of Kabsch it appeared that 

 the movement of this organ was induced and not spon- 

 taneous, but Gad's more recent and complete observations 

 leave no doubt as to its spontaneity. The object of the 

 movement is the scattering of the pollen, and it accordingly 

 begins when the anthers are about to open. The gyno- 

 stemium bends over on to the surface of the labellum, a re- 

 duced segment of the quinquepetalous corolla, which bears a 

 viscid projecting gland : to this the gynostemium adheres 

 until the moment arrives when the internal tensions which 

 tend to straighten it are strong enough to free it from the 

 adhesive surface; the gynostemium is then released with 

 such violence that it swings over to the other side of the 

 flower, at the same time scattering the pollen ; it then slowly 

 curves back again on to the gland of the labellum, and is 

 then in position for a repetition of the movement. No case 

 of spontaneous movement of stamens is certainly known, 

 but Morren fancied he observed something of the kind in 

 Sparmannia and Cereus. 



The foliage-leaves of many plants, particularly of those 

 belonging to the Leguminosae and Oxalidaceae, possess the 

 power of spontaneous movement ; for instance, the terminal 



