GLOSSARY 449 



Sepal. One of the outer circle of leaf-like parts of a flower. Most 



commonly the sepals are comparatively small and green ; but in 



some flowers they are large and white or brightly colored. 

 Sheath. The basal portion of a leaf which more or less surrounds the 



stem, as in the members of the grass family. 

 Sorus. A spot or region in which spores are formed. 

 Species. A name applied to a group of plants so nearly alike that they 



may be referred to by the same name. 

 Spermatium. A small spore-like cell produced in great numbers by 



the wheat rust and many other rusts. The spermatia seem to be 



entirely functionless. 

 Spike. A dense, elongated flower cluster in which the individual 



pedicels are very short. 

 Spikelet. A small or secondary spike ; used in connection with the 



flower clusters of members of the grass family. 

 Spore. A reproductive cell that can develop into a new plant. In 



some of the bacteria, the name is applied to a specially resistant 



condition into which an ordinary cell may pass 4 

 Spore sac. A structure in which spores are borne. 

 Sporidium. One of the kinds of spores produced by rusts. It is borne 



on a very small plant which grows from the germinating winter 



spore. 

 Spring spore. One of the spores of the wheat rust produced on the 



barberry, or the corresponding spore of any other rust ; also called 



an (zciospore or acidiospore. 

 Stamen. One of the parts of a flower which bears pollen ; a microspore 



leaf. 



Staminate. Applied to a flower having stamens but no pistil. 

 Standard. The large upper petal of the flowers of many of the pulse 



family. 



Stigma. The upper part of a pistil, on which the pollen grains land. 

 Stimulus. A change outside a cell or organism which causes a change 



in the processes going on within the cell or organism. 

 Stipule. A leaf-like appendage at the base of a leaf-stalk. 

 Stock. The basal part of a plant (root, or stem and root) upon which a 



graft is made. 

 Strain. A race or breed of plants or animals. Especially applied to two 



sorts (plus and minus strains) to which the plants of the bread mold 



and some of its relatives belong. The difference between plus and 



minus strains is probably a sexual difference. 

 Style. The slender, often hollow, portion of a pistil between the stigma 



and the ovary. 



