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MISC. PUBLICATION 110, U. S. DEPT. OF AGRICULTURE 



tablished as a new, independent 

 plant, as in mosses; an incomplete 

 young shoot, as in grasses. 



Internodes : The portions of a stem be- 

 tween the nodes, or joints 



Interrupted: Not continuous; not uni- 

 form, for example, in density, as an 

 interrupted spike, i. e., a spike which 

 has the flowers in some place or 

 places smaller or fewer in number 

 than elsewhere. 



Introduction: An exotic plant intro- 

 duced by man or other agency from 

 its native region to another. Thus 

 in the United States wheat and the 

 common dandelion are introductions 

 from the Old World. 



Introrse: Turned in; facing inward. 

 Said, for example, of an anther at- 

 tached on the inner side of its fila- 

 ment and facing toward the inside 

 of the flower. 



Involucel : A secondary involucre ; said 

 especially of the whorl of bractlets 

 subtending the umbellets of many 

 umbellifers. (Fig. 36, C, c.) 



Involucre: A whorl of distinct or 

 united bracts or leaves subtending 



Figure 36. — Involucres : A, Flowering 

 dogwood (Corn us florida) ; a, a, a, a, 

 four petaloid involucral bracts form- 

 ing an involucre about tbe central 

 flower cluster ; B, part of flower head 

 of a thistle (Cirsium sp.) ; a, involu- 

 cre, composed of involucral bracts 

 (phyllaries) in numerous rows; C, 

 umbel of carrot (Daucus sp.) ; a, a, a, 

 a, a, pinnatifldly lobed involucral 

 bracts, forming involucre ; o, b, rays, 

 branches, or peduncles of umbel ; c, 

 involucel. composed of involucellar 

 bracts ; d, umbellet 



a flower or flower cluster. The 

 petallike bracts of a flowering dog- 



wood (Cornus spp.) flower cluster 

 are a familiar example of involucre. 

 (Fig. 36, A.) In an umbellifer the 

 involucre subtends the umbel. (Fig. 

 36, C, a.) In a composite the invol- 

 ucre is the usually cup-shaped en- 

 velope of encircling, often imbri- 

 cated (partially overlapping) bracts 

 subtending the flower head. (Fig. 

 36, B, a.) The cup, or cupule, of an 

 acorn is also sometimes referred to 

 as the involucre. . 

 Involute: Inrolled; i. e., with both 

 edges rolled in toward the middle 

 (as a leaf) each edge presenting a 

 spiral appearance in cross section. 

 Isotype: A duplicate of a type speci- 

 men (holotype). A term introduced 

 by F. W. Pennell of the Philadel- 

 phia Academy of Natural Sciences. 

 See paratype and cotype. 

 Katabolism: An alternate spelling for 



catabolism. 

 Keel: A projecting ridge on a surface, 

 like the keel of a boat. When a 

 grass glume or lemma is more or 

 less compressed and boatlike, its 

 midrib, if projecting, is called a keel. 

 The two, often more or less joined, 

 boatlike, forward petals of a pea 

 family corolla are also known as 

 the keel. (Fig. 48, c.) 

 Keeled: Provided with a keel or keels. 

 Labiate: Lipped. A plant of the mint 

 family (Menthacese, or Labiatse), 

 whose members 

 have lipped, or 

 labiate, corollas. 

 Lacerate(d) : Deep- 

 ly and irregularly 

 cut along the 

 edges. 

 Laciniate : Narrowly 

 incised or slashed ; 

 heaving the margin 

 cut into deep nar- 

 row lobes. 

 Lamina: A leaf 

 blade (fig. 37, 5) ; 

 the broader por- 

 tion of a leaf or of 

 a clawed petal. 

 Lanate: Woolly, with 

 dense, long, soft, 

 more or less entan- 

 gled, but not matted ( tomentose ) hairs. 

 Lanceolate: Lance shaped; several 

 times longer than broad and taper- 

 ing from the relatively narrow base 

 to the apex. (Fig. 38. B.) 

 Lanuginous: Downy; beset with fine 



soft hairs ; pubescent. 

 Lateral: Of or pertaining to a side of 



an organism or of its parts. 

 Latex (pi. -tices) : A more or less 

 milky and opaque, usually gummy, 



Figure 37. — Parts 

 of a grass leaf 

 and stem : a, 

 Culm ; o, blade 

 (or lamina; ; c, 

 ligule ; d, sheath 



