44 THE INDIANA WEED BOOK. 



see that it agrees with the weed in hand. If it did not fit a, go to 

 aa and compare. If it is an endogen and listed, it belongs either 

 under a or aa. If it fits aa go to c,, etc. 



If the weed is an exogen, turn to the "Key to the Divisions of 

 Exogens, ' ' and examine the plant for petals to see whether they are 

 present or not. If not present, go to the "Key to the Families of 

 Apetalous Exogens" and try that. If the petals are present see 

 whether they are wholly separate one from another ; if so, go to the 

 "Key to the Families of Polypetalous Exogens." If they are 

 more or less united the plant is gamopetalous and the family should 

 be sought for under the "Key to the Families of Gamopetalous 

 Exogens." Remember that whenever the plant fits a of a key it 

 will run to some family whose name is given between a and aa. If 



Fig. 15. Illustrating the differences between endogens and exogens: a, cross-section of corn-stalk, the dots 

 showing the tops of the long strands of woody fibre scattered irregularly through the pith; 6, parallel reined leaf 

 of an endogen; c, cross-section of stem of an endogen, showing the 4 stem regions, e, the epidermis, c, cortex or 

 bark, w, the wood, p, the pith; d, netted veined leaf of exogen with stipules at base. (After Coulter and Gray.) 



it fits a and 6 it will run to a family between 6 and 66. Whenever 

 it does not fit a letter go to the double of the same letter, and from 

 there on down the key, never backward. If it fits the characters 

 given after a letter, as c y and there is no family name following c 

 then go to d and so on down the key until a family name occurs 

 after a letter. 



As with the endogens, when it runs to a family name turn to 

 the page given and compare carefully the weed with the descrip- 

 tion there given. If the weed agrees with this description then 

 rea.d the descriptions of the different weeds under that family 

 until you find one with which your plant agrees. If the family 

 description does not fit the weed a mistake has more than likely 

 been made in running it into that family. In a work of this kind, 

 where the family descriptions and descriptions of species are neces- 



