Trtassic 



The oldest geologic period in the Mesozoic era; it began 

 about 205 million years ago and lasted for about 40 million 

 years. 



Tribe 



A group of plants of related genera, a division of the 

 Family, e.g., the tribe Festuceae includes the genera Poa, 

 Festuca, Bromus, and others. 



Triploid 



An organism or one of its parts that has three times the 

 Haploid set of Chromosomes in the nucleus, cf. Polyploid. 



Trisomic 



Refers to an organism that has one more Chromosome 

 than the Diploid (q. v.) number; occurs in barley, and peas. 



Tristat Method 



A method of photographing the same area at successive 

 periods of time by permanently marking the spot where 

 each leg of the tripod is set 



Trophic (-trophy) 



Refers to nutrition. 



Trophic Level 



One of the parts in a nutritive series in an Ecosystem 

 (q. v.) in which a group of organisms in a certain stage in 

 the Food chain secures food in the same general manner. 

 The first or lowest trophic level consists of Producers 

 (green plants), the second level of Herbivores, the third 

 level of primary Carnivores, the fourth level of secondary 

 Carnivores. Bacteria and fungi are organisms in the Decom- 

 poser trophic level. 



Trophobiosis 



A type of association of species involving aphids and 

 coccids with ants. cf. Myrmecophilous. 



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