GLOSSARY 503 



Vegetative. — Pertaining to the part of the plant concerned with metab- 

 olism and maintenance of the life of the individual. 



Venation. — The pattern formed by the veins in a leaf. 



Vessel. — Long tube-like structure found in the wood of higher plants, 

 serving for conduction of water. 



Virus. — An infectious substance, the exact nature of which is not well 

 known, since it is invisible under the best microscopes, but which is 

 capable of causing disease in plants and animals. 



Volatile oil. — An essential oil which is highly volatile and can be dis- 

 tilled from plant tissues without being changed chemically. 



Vulcanization. — ^The process of heating rubber in the presence of sulphur 

 to render it a stable substance. 



Whorl. — A circle of structures, such as petals or sepals, in a flower. 

 Wood. — The supporting cells of higher plants, constituting the bulk of 



the root and stem of perennial species. 

 Wood fiber. — Heavily lignified sclerenchyma cells found in xylem of 



Dicots. 



Xanthophyll. — A yellow pigment, composed chemically of hydrogen, 



carbon and oxygen. 

 Xylem. — The water-conducting element of vascular plants. 



Zoospore. — A swimming spore. 



