450 TEXTBOOK OF BOTANY 



Summer spore. A spore produced by the rust on the wheat during the 

 summer, or the corresponding spore of other rusts ; also called a 

 urediniospore or uredospore. 



Tap root. A primary root which persists as the plant grows and which 



pushes directly downward. 

 Tendril. A slender outgrowth, especially of climbing plants, by means 



of which the plant may attach itself to neighboring objects. 

 Terminal. Referring to that part of a structure or organ farthest from 



its place of attachment. 

 Toxin. One of a class of poisonous substances produced by parasitic 



bacteria. 

 Tuber. A thickened portion of an underground stem or branch. 



Umbel. A flower cluster in which all the pedicels arise from the peduncle 

 at about the same level. 



Vacuole. A portion of the protoplasm of a cell, surrounded by a mem- 

 brane, and containing a watery solution of various foods and other 

 substances. 



Variety. A group of plants that are very similar; a sub-division of a 

 species. 



Vascular bundle. A group of conducting cells, consisting either of 

 wood, bast, or both wood and bast. 



Veil. A membrane which for a time attaches the cap of a mushroom 

 to its stalk, and so covers the gills. 



Vein. One of the vascular bundles of a leaf, usually appearing as a 

 light green line. 



Vessel. A long tube produced by the breaking down' of the cross walls 

 in a row of cells. 



Whorl. A circle of three or more leaves borne at the same node. 



Wing. One of the lateral petals of the flowers of many of the pulse 

 family. 



Winter spore. A two-celled spore produced by the rust on the wheat, 

 or the corresponding spore (not in all cases two-celled) of other 

 rusts; also called teliospore or teleutospore. 



Wood. The part of a vascular bundle through which water and dis- 

 solved substances (usually obtained from the soil) are transported ; 

 also called xylem, 



Zygote. A cell produced by the union of. two gametes. 



