KEY TO FAMILIES OP EXOGEN WEEDS. 49 



ad. Ovary inferior or more or less united with the calyx. 



L Flowers not closely bunched into a head which is surrounded by a 

 leafy involucre; those of our weeds mostly 2-lipped, blue or 

 bluish ; stems with an acrid and usually milky juice. 



BELL-FLOWER FAMILY, p. 140. 

 II. Flowers closely bunched into a head surrounded by a leafy in- 



volucre. 



m. Flowers of head all ligulate or split into flat rays (Fig. 10, g.), 

 mostly yellow; juice of stems and leaves milky. 



CHICORY FAMILY, p. 142. 

 mm. Flowers all tubular or only the outer ones of the head with 



rays; juice not or rarely milky. 

 n. Stamens not united by their anthers into a ring or tube 



around the style. 



o. Leaves all opposite, their ribs and the flower-stalks 

 prickly; heads very large, oblong-cylindrical, with nu- 

 merous long spiny-tipped awns ; flowers all perfect. 



TEASEL FAMILY, p. 139. 



oo. Leaves alternate, mostly divided or lobed, not prickly; 



staminate and pistillate flowers of our weeds in sepa- 



rate heads on the same plant, the latter without a 



corolla. RAGWEED FAMILY, p. 149. 



nn. Stamens united by their anthers into a tube or ring about 



the style; fruit or so-called seed an achene, usually bear- 



ing a tuft of hairs or several awns. (Figs. 10, a; 11, /, g.) 



THISTLE FAMILY, p. 153. 



The arrangement and names of the weeds listed are mainly 

 those of Britton and Brown's ''Illustrated Flora of the Northern 

 States and Canada." This is a work of three volumes published 

 by Chas. Scribner's Sons, N. Y., and is the only systematic botany 

 in which all species described are figured. Twenty-five of the 

 illustrations used in this book were taken from it. The others are 

 from the works of the various authors whose names are mentioned 

 under the respective figures. 



At the end of the descriptions will be found a list of the princi- 

 pal books or papers which have been used in the preparation of 

 this work, and also a glossary of the more important botanical 

 terms which have been used. 



The first letter in the parenthesis after the common names of 

 each weed listed shows whether the plant is an annual (A.), a bi- 

 ennial (B.) or a perennial (P.). The second letter denotes whether 

 it is introduced (I.) or native to Indiana (N.). The figure 1, 2 or 

 3 shows the class to which the weed has been assigned by the 

 writer, (See p. 12). Thus, 1 denotes that the weed belongs to 

 Class I., 2 a weed of Class II. and 3 a weed of Class III. 



141 



