DEVELOPMENT OF PLANTS 



409 



anther is sessile upon it (Fig. 292, B). One or two of the stig- 

 mas are generally modified into a mucilage-secreting organ, called 

 the rostellum (Fig. 293, A). The microspores are usually united 

 into a waxy mass, pollinium (pi. pollinia) and attached to a 

 sticky part of the rostellum (Fig. 293, B, C). The remarkable 

 feature about these gaudy flowers is the relation that the label- 

 lum, anther, rostellum and stigma sustain to each other. The 

 position of these organs is such that an insect visiting the flower 



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 C, one of the pollinia withdrawn from the anther show- 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. 



touches with some part of his body the sticky part of the rostel- 

 lum and the pollinia are thus made fast to him and carried to the 

 stigma of another flower. These devices are so elaborate in 

 many orchids that the microspores can only reach the stigma 

 through the agency of an insect. In the lower types of orchids, 

 as the moccasin flower (Fig. 292, B), a somewhat different 

 arrangement is found. The bee enters the opening in the upper 

 part of the labellum and feeds upon the glands distributed along 



