274 GLOSSARY AND INDEX. 



reticulate-veined leaves, stem witli open fibro-vascular bundles ar- 

 ranged in a cylinder, and flowers commonly on the plan of five. 



didynamous, having four stamens, one pair longer than the other. 



dimorphic, existing under two distinct forms, 86. 



dioecious, having male and female reproductive bodies on different indi- 

 viduals, 85. 



disk flower, one of the tubular flowers belonging to the disk or central 

 part of a radiate composite head. Heads that have only tubular 

 flowers are said to be discoid, those having only strap-shaped flowers 

 are said to be ligulate, 258. 



dispersal, 17. 



divided, cut to the midrib or base, 58. 



dorsal, pertaining to the back ; the lower, or outer, surface of a leaf is 

 said to be dorsal in distinction from its upper, or ventral, surface ; 

 the upper green surface of the flat thallus of a liverwort is said to be 

 dorsal in contrast with the lower, or ventral, surface from which 

 roots arise. 



dorsi-ventral, having a back, or dorsal, and a front, or ventral, surface or 

 aspect, with a different anatomical structure and different reactions 

 toward light and gravitation. 



elater, one of the appendages of spores of Equisetum. The term is also 



applied to other hygroscopic structures that aid in the dissemination 



of spores, 139. 

 embryo, 14, 78. 

 embryo-sac, the sac, commonly a single cell, in which the oosphere and 



flnaUy the embryo is formed, 78, 95. 

 endocarp, inner layer of the pericarp, 92. 

 endopleura, inner seed-coat, 3. 

 endosperm, tissue containing nutritive materials surrounding the embryo 



and enclosed in the embryo-sac, 3, 84. 

 endospore, the inner coat of a spore, 132. 

 entomophilous, fertilized by the agency of insects, 

 environment, the sum total of external agents and iafluences affecting an 



organism, 

 epidermis, the protective layer (sometimes layers) of cells covering the 



surface of a plant, 43, 59, 61. 

 epipetalous, inserted on the petals, 257. 

 epiphragm, a membrane extending across the mouth of the capsule of 



certam mosses, 124. 

 epiphyte, a plant growing upon another, but not parasitic, 179. 

 equitant, astride, the peculiar arrangement of leaves seen in the Iri- 



dacese, 172. 



