Air-sacs 



Thin-walled structures, containing air, in birds and in 

 some insects. 



Alar, Alary, Alate 



Winged. 



Albinism 



Complete or almost complete absence of pigment, result- 

 ing in plants that are white in whole or in part, and in 

 animals with milky-white skin, light hair, and red pupils 

 in eyes. 



Albino 



An organism deficient in pigment. 



Alice's Principle 



The extent of aggregation and the degree of density 

 of a population most favorable for optimum growth and 

 survival varies according to the species and environmental 

 conditions. Either deficiency or excess may be detrimental. 



Aletophyte 



A weed growing in a mesic (q. v.) habitat. 



Algae 



The simplest kind of green plants, usually growing in 

 water or damp places, consisting of several phyla, formerly 

 classified in the Thallophytes (q. v.). 



Algoid 



Resembling an alga. 



Algology 



The study of Algae. 



Alien 



An introduced plant which has become naturalized. 



11 



