624 



APPENDIX A 



bulb or some other form of underground stem. Asparagus, onion, trillium, lily-of- 

 the-valley, true lilies, tulip, and dogtooth violet are members of this family. 



The Orchidaceae (orchid family) is the most advanced and specialized of all 

 the families of monocotyledons and is largest in number of species, though not to 

 be compared with the Gramineae in number of individuals. The flowers of orchids 

 are highly modified in relation to various special arrangements for pollination by 

 particular kinds of insects or by hummingbirds (Fig. 17.18). Aside from their 



Fig. A. 25. A native orchid, the yellow lady's-slipper, Cypripedium calceolus. (Photo by Prof. 

 E. B. Mains.) 



value as ornamental plants, orchids are of little economic importance; the only 

 one that plays a part in ordinary commerce is a Mexican species from which 

 vanilla is obtained. 



The Dicotyledons (subclass Dicotyledoneae, commonly called dicots) are a much 

 larger assemblage than the monocots, with about 106,000 known species. Two 

 great sections or series can be distinguished, based upon the characteristics of the 

 flower. In Series I (Archichlamydeae) the petals are either separate (Polypetalae) 

 or absent (Apetalae). In Series II (Metachlamydeae) the petals are partly or 

 completely fused into a tube around the stamens and pistils (Sympetalae). The 

 two series are also distinguished by various other differences. 



Series I. Among the families of this assemblage are several small ones that 

 include some of our common hardwood trees with wind-pollinated, inconspicuous 



