392 



THE ORCHIDALES 



flower. In the higher types of orchids, the insect probing for 

 the nectar touches the sticky discs of the rostellnm, to which the 

 pollinia are attached, and in this way they are fastened to his 

 body and drawn out of the open anthers when he leaves the 

 flower (Fig. 293, C). In some cases the pollinia quickly curve 

 after being withdrawn from the anther, with the result that this 

 change of position brings them into line with the stigma of the 

 next flower visited. In other genera certain cells are irritable 



Fig. 293. Higher type of the Orchidales : A, flower of Orchis — /, label- 

 lum; p, the two unmodified petals; s, sepals; r, rostellnm to which the 

 two pollen masses, pollinia, in the two-lobed anther, an, are attached by 

 sticky discs; st, stigma. B, enlarged lateral view of the anther which has 

 opened, exposing the pollinia. C, one of the pollinia withdrawn from the 

 anther, showing adhesive disc at base which is attached to the rostellnm. 

 At right a pollinium enlarged, showing the small masses of microspores, 

 massula, that may be separately detached from the pollinium. — After 

 Warming. 



and in a high state of tension. A touch causes an explosion that 

 results in hurling out the pollinia which always land on the end 

 to which the sticky disc is attached and so become fastened to the 

 insect. (See Darwin's Fertilization of Orchids for a discussion 

 of the multiplicity of these arrangements. ) 



The seeds are among the most rudimentary of the Spermato- 

 phyta, consisting of an undifferentiated, few-celled embryo with- 



