270 



GEXERAL BIOLOGY 



FIG. 165. Leaves of the smooth sumac, showing variation, a, the 

 normal odd pinnate leaf; 6, an abrupt pinnate leaf; c and d, 

 intermediate forms (in the tabulation, such were counted for the 

 whole number to which they most nearly approximated) ; e, an odd- 

 pinnate leaf with a leaflet of one pair omitted (of rare and prob- 

 ably accidental occurrence) , / and g, leaves from the base of the 

 fungus gall that is shown in fig. 28, page 3 7, snowing a tendency 

 (under the stimulus of the parasite), to be more compound. 



