DEVELOPMENT OF PLANTS 



425 



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 after being withdrawn from the anther, with the result that this 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

 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 



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

 lum; p, the two unmodified petals; s, sepals; r, rostellum 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 C, one of the pollinia withdrawn from the anther show- 

 ing adhesive disc at base which is attached to the rostellum. At right a 

 pollinium enlarged, showing the small masses of microspores, massula, that 

 may be separately detached from the pollinium. — After Warming. 



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- 

 out endosperm and surrounded by a delicate bladder-like integu- 

 ment. They are exceedingly small and produced in enormous 

 numbers; in fact, the seeds of the rattlesnake orchid, Peramium, 

 weigh but two millionths of a grain each and float in the air like 



