reach of the livestock that may be grazed without permanent 

 deterioration of the plants of this species or associated 

 species nor of the soil. cf. Overstocking. 



Protandrous 



Refers to a flower that produces pollen before the stigma 

 is receptive, e.g., fireweed; or to animals that produce sperms 

 sooner than eggs are produced by the same animal, e.g., 

 certain nematodes. cf. Protogynous. 



Protective Coloration 



The concept that coloration in animals benefits the 

 individual by affording concealment from predators or from 

 prey animals, cf. Mimicry. 



Protein 



A nitrogenous organic compound of large molecular size 

 and complex structure, formed from amino acids. 



Proterozoic 



The geological era preceding the Paleozoic which began 

 about 2,000 million years ago and lasted for about 1,500 

 million years. 



Prothallus 



The vegetative structure of the Gametophyte (q. v.) gen- 

 eration that is part of the life cycle of ferns and their allies, 

 cf. Thallus. 



Protista 



A group including all one-celled organisms such as one- 

 celled algae, bacteria, and protozoans; suggested as a third 

 kingdom of living organisms, the other two being plants 

 and animals. 



Protocooperation 



An interaction between organisms that is mutually bene- 

 ficial but not obligatory to those participating, not appli- 



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