452 APPENDIX 



SPINDLE. The 'fiber-like' apparatus between the centrosomes 

 during mitosis. 



SPIREME. The linear arrangement of the chromosomes frequently 

 observed during mitosis. 



SPLEEN. A vascular ductless organ of most Vertebrates, usually 

 situated near the stomach, which produces certain changes in 

 the blood. 



SPONTANEOUS GENERATION. See Abiogenesis. 



SPORANGIUM. A spore-producing structure on a sporophyll. 



SPORE. A cell, liberated from the parent, which gives rise without 

 fertilization to a new individual. The resistant phase assumed 

 by certain unicellular organisms; e.g., Bacteria. 



SPOROPHYLL. A leaf which bears sporangia. 



SPOROPHYTE. Spore-bearing (asexual) generation in plants exhibit- 

 ing alternation of generations. 



SPORULATION. Occurrence of several simultaneous divisions by 

 which a unicellular organism is resolved into many smaller cells. 



STAMEN. The pollen-bearing organ in Flowering Plants. A micro- 

 sporophyll. See Anther. 



STELE. The central cylinder of root and stem, formed of united vas- 

 cular bundles, in the highest Flowering Plants. 



STIGMA. The tip of the pistil adapted to receive the pollen and pro- 

 vide for its germination. 



STIMULUS. Any condition which calls forth a response from living 

 matter. 



STIPULES. Pair of appendages frequently occurring at the point 

 (leaf base) where the petiole joins the stem. 



STOMATA. Openings through the epidermis of a leaf for the inter- 

 change of gases and exit of water vapor. The 'stomatic ap- 

 paratus' comprises the stoma and its guard cells. 



STYLE. An elongation of a pistil which bears the stigma. 



SYMBIOSIS. The association of two species in a practically obliga- 

 tory and mutually advantageous partnership; e.g., Lichens. 



SYMPATHETIC NERVOUS SYSTEM. See Autonomic. 



SYNAPSE. The contact of one nerve cell with another, which makes 

 possible the conduction of a nervous impulse from cell to cell. 



