76 THE PLANT WORLD. 



anther. The two matched petals, long, narrow and curved, stand 

 beside the column, their extremities projecting- and forming an 

 arch, in such a way as to leave a three-sided opening between 

 petals and anther ; while the third petal stands away from the 

 column, the narrow stalk adherent to the calyx, the roughly trian- 

 gular blade free and pendant from a point within the margin. 

 The unmatched petal, the lip or labellum, of orchid flowers, is 

 usually larger and more highly modified in form and brilliant in 

 hue than the petals, and is usually so placed as to serve as a land- 

 ing stage for visiting insects, often with bosses and ridges for 

 secure footing, often also with some sac or spur at the base for 

 nectar. The lip of Masdcvallia inuscosa adds still another dis- 

 tinction ; for besides being expanded and hollowed and bearing 

 cushions of deep maroon hairs, its blade is irritable and full of 

 lively motion. 



When a flower first opens, the tails of the sepals curve back 

 and the labellum is seen with its bearded tip folded just beneath 

 the arch of the petals. Presently, however, the blade descends, 

 turning by a flexible neck, or hinge, until it stands in the position 

 represented in the right-hand flower of our plate. If the surface 

 is now very gently touched, almost instantly the lip springs up, 

 rising slowly for a moment and then shutting with a sna]). The 

 blade fits the walls of the calyx and the curve of the petals so 

 that a space is enclosed, open nowhere except at one point, where 

 the arched petals extend beyond the column. The highest flower 

 (Fig. 13) shows this aperture as a dark spot. In newly opened 

 flowers in warm moist air the whole operation may take as little 

 as two seconds. After a few minutes — usually fifteen to twenty — 

 the lip again falls, but very gradually, and immediately is ready 

 for a repetition of the performance. A flower on our greenhouse 

 plant responded many times a day without loss of sensibility ; in 

 fact after repeated stimulation the lip opened out somewhat sooner 

 than before. 



The whole surface of the labellum is not sensitive. Touches 

 anywhere except upon a median ridge, or cushion {cv. b^ig. 14, 

 A), produce no efl^ect. But the lightest brushing of this crest 

 with a hair suffices to set off the mechanism of movement. Hence 



