GLOSSARY 253 



Variety. A subdivision of a species. 



Vein. A fibro-vaseular bundle of a leaf, petal, or other thin and flat 

 organ. 



Venation. The manner in which veins are distributed. 



Venter. The swollen basal portion of an archegonium containing the egg. 



Vernation. The manner of unfolding in buds. 



Vessel. A tube or duct made of separate sections but continuous from 

 the absorption of the cross partitions. The walls have various 

 thickening deposits, often spiral or ring-formed. 



Volva (a wrapper). An envelope inclosing a young toadstool and rup- 

 tured by the growth of the latter, portions sometimes remaining as 

 scales on the top of the cap and sometimes as a cup at the base of 

 the stalk. 



Xerophyte (dry plant). A plant which can live with a scanty supply of 



water. 

 Xylem (wood). The wood or inner part of a flbro-vascular bundle, the 



portion within the bundle cambium. 



Zone. In ecology a band of any given plant formation, usually bounded 



by other bands representing other formations, as about a pond, a 



salt spring, etc. 

 Zoospore (animal spore). A ciliated and therefore motile asexual spore. 

 Zygomorphism (yoke form). The arrangement of parts in corresponding 



right and left halves ; bilateral symmetry. 

 Zygospore (yoke spore). A sexually formed spore resulting from the 



fusion of similar gametes (isogamy) ; also called a zygote. 



