GLOSSARY OF BOTANICAL TEEMS 



11 



Dendrology: That port of botany 

 which deals with trees. Ordinarily 

 the term is confined to taxonomic 

 and morphological investigations of 

 trees, other phases of tree science 

 being dealt with by forestry, arbori- 

 culture, horticulture, ecology, phyto- 

 pathology, etc. 



Density: The relative degree to which 

 vegetation covers the ground sur- 

 face, and often expressed in tenths, 

 1.0 indicating a complete ground 

 cover of such vegetation. Specifi- 

 cally in range reconnaissance in the 

 Forest Service, " average density " 

 is a term used to indicate the pro- 

 portion of ground surface actually 

 covered by herbaceous or shrubby 

 vegetation within reach of livestock, 

 the lateral spread of the plant foli- 

 age, stems, and branches above 

 ground being carefully considered. 

 The density of grasses is based on 

 the spread when the plants are 

 grazed to the proper extent rather 

 than on the normal plant spread 

 when ungrazed or the reduced 

 spread when total use has been 

 made of the plant. The density of 

 erect weeds is based on the amount 

 of ground that appears covered 

 when the vegetation is viewed from 

 directly above. The density of 

 browse is estimated from the ground 

 surface covered by that part of the 

 browse that is readily accessible to 

 livestock. 



Dentate: Toothed, with the "teeth" 

 nearly equal sided, projecting for- 

 ward or at a right angle rather than 

 upward, and usually being acutish. 

 (Fig. 30, C.) 



Denticulate: Minutely dentate. 



Depauperate: Dwarfed, starved. Said 

 of small, impoverished, undeveloped 

 plants grown in poor soil or under 

 otherwise unfavorable conditions. 



Depressed: Vertically flattened; i. e., 

 as if pressed downward from above. 



Determinate: Having a centrifugal in- 

 florescence, the order of flowering 

 being from the center outward or 

 from above downwards, the main 

 axis terminating in a flower. Lit- 

 erally terminated or ended, the main 

 axis of the inflorescence being 

 estopped from further growth. The 

 cyme is probably the most familiar 

 example of determinate inflores- 

 cence. 



Dextrorse: Spirally twisting to the 

 right. Said of vines that twine 

 counterclockwise, as dodder and 

 hops. 



Di-: A prefix (Greek) signifying two, 

 or double. 



Diadelphous : Having the stamens more 

 or less united by their filaments into 

 two groups, or clusters; literally, 

 two brotherhoods. The stamens of 

 most clovers and of many other leg- 

 umes are diadelphous. 



Dichotomous: Two-forked, the forks, 

 or branches, regular and nearly 

 equal. 



Dicotyledon: A plant whose embryo 

 and germinating seedling has two 

 cotyledons, or seed leaves. The 

 dicotyledons form one of the two 

 main groups into which angiosperms 

 are separated, the other being mono- 

 cotyledons. 



Didynamous: Having four stamens ar- 

 ranged in two pairs, one pair 

 noticeably longer than the other. 

 For example, the stamens of many 

 members of the figwort family 

 ( Scrophulariacese) are didynamous. 



Diffuse: Loosely, widely, and irregu- 

 larly spreading, the branches usu- 

 ally numerous. 



Digitate: Fingerlike; compound with 

 similar parts radiating from a com- 

 mon point; as the digitate leaflets 

 of lupine. (Fig. 28.) The same as 

 palmate. 



Figure 28. — Digitate leaf of lu- 

 pine (Lupinus) 



Dioecious: Literally, in two houses. 

 One-sexed ; male or female only, the 

 staminate (male) and pistillate 

 (female) flowers borne on different 

 individual plants. The flowers of 

 buffalo grass (Bulbilis), for exam- 

 ple, and of many ashes (Fraxinus 

 spp.), maples (Acer spp.), and hol- 

 lies^ (Ilex spp.), are dioecious. 



Discoid: Disklike, or lacking ray flow- 

 ers. Said of composites that have 

 only centers, or disk flowers, in the 

 flower heads, like the common nig- 

 gerhead (Rudbeckia, ocoidentalis) . 



