692 PAET IV. THE PHYSIOLOGY OF PLANTS. 



of pollination (see p. 452), to the distribution of the seed, etc. 

 It is impossible to enter upon a further consideration of the 

 biology of the flower, but the phenomena of movement presented 

 by the essential floral organs deserve special mention. 



A remarkable case of spontaneous movement is that of the 

 gynostemium of Stylidium (Candollea) adnatum, the object of 

 which is the scattering of the pollen, and it accordingly begins 

 when the anthers are about to dehisce : the gynostemium bends 

 over till it touches a gland on the anterior petal, and to this it 

 adheres until it straightens and frees itself from the stioky gland 

 with a jerk which scatters the pollen ; the movement is then 

 repeated. 



Induced movements are more common. Thus the two lobes of 

 the stigma (e.g. Mimulus, Bignonia, Martynia), close together on 

 being touched : the movement doubtless ensures the adhesion of 

 the pollen brought by an insect. The stamens are irritable in 

 many plants. For instance, in Berberis, when an insect touches 

 the irritable base of one of the nearly horizontal stamens, the 

 stamen rises up on its point of attachment as on a hinge, and 

 strikes the insect with the anther, thus dusting it with pollen. 

 Again, the syngenesious stamens of Centaurea (p. 664) shorten 

 on stimulation by touch : the flower is protandrous ; consequently, 

 as the filaments contract, the pollen shed by the coherent anthers 

 is pushed out of the open end of the anther-tube by the style 

 within, and is removed by the insect. 



CHAPTER II. 



/ 



SPECIAL PHYSIOLOGY OF THE NUTEITIVE FUNCTIONS. 



6. Absorption. The food of plants is absorbed, generally 

 speaking, either from the soil or from the air. 



Plants which do not possess chlorophyll (e.g. Fungi) usually 

 obtain the whole of their food from the soil ; whereas plants which 

 do possess chlorophyll absorb from the air one of the most im- 

 portant constituents of their food, namely carbon dioxide. 



In exceptional cases it is obtained from other sources; for 

 instance, parasitic plants absorb their food from the hosts upon 

 which they live, and the " insectivorous " plants absorb a portion, 

 at least, of their food, from the insects which are caught by their 



