Summation Temperature 



See Temperature summation. 



Summer Fallow 



The cultivation of a field in which crops have not been 

 planted in order to control weeds and to accumulate soil 

 moisture for the growth of a crop subsequently, cf. Fallow. 



Summer Wood 



The less porous and harder portion of the Xylem (q. v.) 

 of a growth layer in woody plants produced in the latter part 

 of the growing season, cf. Spring wood. 



Sun Plant 



A plant that grows well in full sunlight, cf. Heliophyllous. 



Sunscald 



Death of tissues of a plant caused by high temperature 

 and loss of water in organs exposed to bright sunshine. 



Sunspot Cycle 



The alternation in occurrence of a period of numerous 

 spots on the surface of the sun and a period with fewer 

 spots; one cycle averages about 11 years. 



Super-organism 



See Epiorganism. 



Superparasite 



A secondary Parasite, i. e., a parasite using another as its 

 Host. 



Supersonic 



Refers to vibrations exceeding 20,000 per second, not 

 audible to the human ear. 



Superspecies 



A group of related Species that are geographically iso- 

 lated; without any implication of natural Hybridization 

 among them. cf. Syngameon. 



334 



