410 THE ORCHIDALES 



the bottom. In leaving the flower he forces his way through 

 the small opening on either side of the style and so he first comes 

 in contact with the stigma and later with the anthers, which are 

 two in number and located back of the stigma. In this flower 

 the anthers are surrounded by a sticky mass and the microspores 

 are thus fastened to the insect's body to be carried to another 

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

 the nectar touches the sticky discs of the rostellum, 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 after being withdrawn from the anther, with the result that this 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 

 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 undififerentiated, 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 

 dust particles. The fringed orchis (Blephariglottis) , Arethusa, 

 ladies' tresses (Gyrostachys) , rattlesnake plantain (Peramium), 

 grass pink (Limorodum), rose pogonia, showy orchis (Gale- 

 orchis), moccasin flower (Cypripediiim) are among the common 

 and more showy of our native orchids. 



Class B. Dicotyledones 



136. General Characters. — ^The structure of these plants is 

 more complex than that of the monocotyledons and their varia- 

 tions have been more extensive and successful, over 100,000 

 species being known. For this reason they are adapted to a 

 greater range of conditions and have become the dominant plants, 



