THE ORCHIS FAMILY. 155 



XX. THE ORCHIS FAMILY. ORCHIDACEJE. 



MATERIAL REQUIRED. 



Yellow lady's-slipper, Cypripedium pubescem, Willd., and Arethusa, 

 Arethusa bulbosa, L., in flower. Other species of Cypripedium may 

 be substituted for the former, and Calopogon or Pogonia for the lat- 

 ter. If it is impossible to obtain indigenous species, various trop- 

 ical orchids can be procured through florists in the larger cities, 

 who will deliver them safely at a distance. The expense is of 

 small moment compared with what is gained by having a familiar 

 acquaintance with at least two or three representatives of a family 

 of plants in which mechanical contrivances for securing cross- 

 fertilization have been carried to the highest degree of perfection. 



YELLOW LADY : S-SLIPPER. Cypripedium pubescens, Willd. 

 Flower. 



Our study will be restricted to the flower, which, though 

 greatly modified, has departed from the type less than those 

 of other genera, and remains " as a record of a former and 

 more simple state " of the great family to which it belongs. 1 



I. Notice first the most conspicuous external features. 



1. The nodding flower, generally single, terminating 



the leafy stem. 



2. The floral envelopes. 



a. Three sepals, of which the upper one is the 

 largest, the two lower united into one, but 

 showing at the apex a trace of their original 

 separation. 



1 Darwin, Fertilization of Orchids, p. 226. 



