ADAPTATIONS FOR INTERCROSSING. 



231 



stigma by the same upward movement which immediately after- 

 ward raises the anther-lid and carries away its pollen, to be 

 transferred to a third blossom, and so on. 



422. But it is in Orchis 

 and in the commoner re- 

 presentatives of Orchis in 

 North America (viz. Ha- 

 benaria, &c.) that the 

 most exquisite adapta- 

 tions are found, and the 

 greatest economy se- 

 cured ; paralleled, how- 

 ever, by most of the very- 

 numerous and various epi- 

 phytic and by various ter- 

 restrial Orchids of warmer 

 regions. A single illus- 

 tration may here suffice ; 

 and Darwin's volume on 

 the Fertilization of Or- 

 chids (396, note), with 

 its references to the 

 copious literature of the 

 subject, may be studied 

 for full particulars and 

 their bearings. The flower 

 is trimerous, and the peri- 

 anth adnate to the ovary, 

 therefore apparently de- 

 veloped upon its sum- 

 mit. The three external 

 parts of the perianth, 

 which in Habenaria orbi- 

 culata (Fig. 460) are 

 much the broader, are the 

 sepals: the three alternate 

 and internal, the petals : 

 the base of the long and narrow petal which is turned downward 

 is hollowed out and extended below into a long tube, closed at 

 bottom, open at top (the spur or nectary), in which nectar is 



FIG. 460. Flower of Habenaria or Platanthera orbiculata, enlarged. 461. Combined 

 stamen and stigma, more enlarged. 462. One of the two pollen-masses (pollinia), with 

 its stalk and glutinous disk or glaud. 462. Lower part of this stalk and ita diak, more 

 magnified. 



