GLOSSARY 443 



Velum. A nienil)ranou.s partition or oovoring resembling a veil or curtain, especially 



the membrane covering the gills in an immature mushroom. 

 Venation. The arrangement or system of veins or vascular bundles in a leaf blade. 

 Venter. The enlarged basal portion of an archegonium enclosing the egg. 

 Ventral. Pertaining to the front or inner side of an organ; designating the surface 



toward the axis, as the upper side of a leaf; in liverworts and ferns, pertaining 



to the lower side of the prothallium. 

 Vermiform. Worm-like. 



Vernation. The arrangement of foliage leaves within a bud. 

 Vessel. A water-conveying duct composed of a row of thick-walled, nonliving cells 



that have lost their end walls; one of the cells forming such a duct. 

 Volva. A cup at the base of the stipe in certain mushrooms. 



Whorl. A circle of similar parts about the same point on an axis. 



Xanthophyll. Any of a group of mainly light yellow pigments found in various plants, 

 eitlier alone or associated with others, particularly chlorophyll; they differ from 

 carotins in containing oxygen as well as carbon and hydrogen. 



Xylem. In vascular plants, a complex tissue consisting of tracheids, vessels, or both, 

 and often also of wood fibers and parenchyma, and serving for the conduction of 

 water and for mechanical support; woody tissue. 



Zoospore. A naked spore with cilia, by the vibration of which it moves. 

 Zygomorphic. Having bilateral symmetry, the parts arranged symmetrically on 



either side of a median longitudinal axis. 

 Zygote. A cell formed by the fusion of two gametes. 



