860 Appendix 



Thallophyta (thai -of i ta) (Gr. thallos, young shoot or branch; phyta, plant), 



simple, thallus plants without true leaves, stems, or roots. 

 Thallus (thai' us) (L. thallos, a. shoot), simple, undifferentiated plant. 

 Thermotaxis (thur mo -tack' sis) (Gr. therme, heat; taxis, response), reaction to 



heat or cold. 

 Thermotropism (thur -mot' ro pizm) (Gr. thertne, heat; trope, turn), see Thermo- 

 taxis. 

 Thigmotaxis (thig mo -tack' sis) (Gr. thigema, touch; taxis, arrangement), motile 



response to contact or touch. , 



Thigmotropisni (thig -mot' ro pizm) (Gr. thigema, touch; trope, turn), response 



to contact. 

 Thoracic (tho -ras' ik) (Gr. thorax, chest), pertaining to thorax (chest). 

 Threshold (thresh' old) (A.S. therscold, starting point), minimum amount of a 



stimulus to get response. 

 Thrombin (thromb' in) (Gr. thrombos, clot), substance to aid blood clot formation. 

 Thymus (thy'mus) (Gr. thymos, thymus), ductless gland in the pharyngeal region 



of vertebrates. 

 Thyroid (thy' roid) (Gr. thureos, shield; eidos, resemble), ductless gland in the 



neck of vertebrates which regulates metabolism, growth, etc. 

 Thyroxin (thy -rok' sin), hormone produced by the thyroid. 



Thysanura (thi sa -nu' ra) (Gr. thysanos, fringe; oura, tail), order of wingless in- 

 sects such as bristletails. 

 Tibia (tib'ia) (L. tibia, pipe), larger, inner bone of the lower leg of vertebrates. 



The part between the femur and tarsus of an insect leg. 

 Tissue (tish' u) (Fr. tissu, woven), group, of similar cells performing a specific 



function. 

 Toxin (tok' sin) (Gr. toxicon, poison), chemical substance of bacterial origin 



which stimulates animal protoplasm to produce a specific antitoxin (against 



toxin) . 

 Trachea (tra' ke a) (Gr. tracheia, windpipe), tube to carry air. 

 Tracheal tube (tra' ke al) (Gr. tracheia, tube), rather long tube of the plant 



xylem composed of sev^eral hollow cells fused end to end. 

 Tracheid (tra'ke-id), single, hollow, enlongated plant cell with pitted walls (in 



the xylem) to conduct materials. 

 Tracheole (tra'keol), small tracheal tube. 

 Tracheophyta (tre ke -of i ta) (Gr. tracheia, tube; phyta, plants), subphylum of 



plants possessing vascular tissues. 

 Transformism (trans -form' izm) (L. trans, over; forma, form), the doctrine that 



species may change to form new species, as opposed to special creation or 



fixism. 

 Translocation (trans lo -ka' shun) (L. trans, beyond; locus, place), transfer of 



soluble materials through the sieve tubes of the phloem of vascular plants; 



the exchange of parts of chromosomes. 

 Transmutation (trans mu -ta' shun) (L. trans, over; mutare, change), ability of 



genes to change their position, as in translocation from one chromosome to 



a nonhomologous one. 

 Transpiration (trans pi -ra' shun) (L. trans, through; spiro, breathe), loss of 



water from plants, especially from leaves. 



