Ontogeny 



The development of an individual, or a part of it, from 

 the Zygote to the adult, cf. Phytogeny. 



Oogamy 



Sexual reproduction by means of eggs and sperms, cf. 

 Heterogamy. 



Open Community 



A community in which the plants are more or less scat- 

 tered, in which invasion may readily occur. 



Open Pollination 



Pollination (q. v.) by wind, insects, etc., not directly by 

 man. 



Open Range 



An extensive grazing area on which the movements of 

 livestock are unrestricted. 



Open Woodland 



A parkland type of vegetation in which trees do not form 

 an open canopy. 



Optimum (Conditions) 



The range of conditions which is most favorable for an 

 organism, or for a certain function of an organism, cf. Eco- 

 logical amplitude. 



Order 



In plant and animal Taxonomy, a group or Taxon of 

 related families, e. g. Resales. In phytosociology, a group of 

 similar Alliances. In classification of soils, the highest cate- 

 gory comprising Zonal, Intrazonal, and Atonal soils. 



Ordovician 



A geological period in the early pan of the Paleozoic 

 era, which began about 425 million years ago and lasted 

 about 65 million years. 



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