KEY TO THE SPECIES 83 



4. LACTUCA (Wild Lettuce) 



Tall herbs with milky juice, alternate leaves, cylindrical involucre of unequal 

 imbricated bracts, rays truncate-toothed at apex, and ribbed acheues narrowed 

 into a beak which is expanded at summit Into a flat disk bearing the Abundant 

 pappus. 



1. tactuca pulcliella (Pursh) DC. (Blue Lettuce). A glabrous perennial 

 with slender leafy stem., 2-4 dm. high, simple except the corymbose- panicle of 

 showy blue heads ; leaves lanceolate or oblong, entire, toothed or pinnatifid ; 

 achenes flat, oblong, 3-i mm. long, longer than the beak ; pappus abundant, soft 

 and white. 



LXVII. COMPOSITiE (Composite Family) 



The greatest family of the flowering- plants, chiefly bloom- 

 ing in summer and autumn, with flowers collected in a head 

 which is surrounded by a rosette of bracts (involucre), the mar- 

 ginal flowers (rays) usually with strap-shaped conspicuous 

 corollas, the inner flowers (forming the disk) tubular and 5- 

 toothed, calyx in the form of hairs, bristles, teeth, scales, etc. 

 (pappus), 5 stamens united by their anthers, a 2-cleft style, and 

 an inferior ovary becoming a dry seed-like achene. (See Plant 

 Structures, p. 275 ; also p. 276, Fig. 261.) 



* Disk flowers yellow ; ray not yellow. 



-H Receptacle naked ; pappus of capillary or rigid scabrous bristles. 



1. Townsendla. Pappus bristles few, rigid and scabrous ; style appendages 

 lanceolate"; achenes flattened, with thick margins, those of the ray triangular ; 

 rays white, blue or purple. 



2. Erigeron. Pappus bristles numerous, capillary; style appendages short, 

 rounded ; achenes 2-nerved ; rays variously colored. 



-*- T- Receptacle chaffy; pappus wanting. 



3. Achillea. Involucre campanulate, its inner bracts membranous — like the 

 bracts of the receptacle ; rays white, short and broad ; leaves dissected. 



» * Disk flowers white or pinkish ; rays wanting or (if present) white and 

 inconspicuous. 



4. Chaenaetis. Leaves pinnately dissected ; pappus of hyaline scales. 



5. Petasites. Root-leaves large, sagittate ; pappus of numerous long white 

 capillary bristles. 



* * * Ray flowers yellow. 



■H Receptacle chaffy ; pappus of 2-pointed scales or wanting ; achenes more 

 or less 4-angIed. 



6. Kudbeckia. Disk hemispherical or conical, brownish-black ; pappus 

 wanting ; involucre of spreading leaf-like bracts. 



7. Helianthug. Disk flat, brownish or dark purple ; pappus 3 scarious 

 deciduous scales, involucre of spreading attenuate bracts. 



