THE WILLOW FAMILY. 183 



I. Note first their external characters and habits, and 

 notice in what respects they differ from those of the wil- 

 lows. Compare 



1. Bark. 



2. Buds, particularly the surface of the bud-scales. 



3. Leaves. 



4. Branches, as to size, texture, and surface marking. 



II. Carry out, step by step, a thorough comparison of 

 the inflorescence and flowers. 



1. How do the scales of the poplar catkin differ from 



those of the willows? 



2. Do the flowers of the poplar have any structure that 



is wanting to those of the willows ? 



3. Compare the number of stamens in the two genera. 



4. Are their fruits and seeds essentially alike ? 



III. Finally, after several species of each have been 

 studied, record all the characters in which willows and 

 poplars agree. The characters exhibited by all of them in 

 common are those of the willow family (Salicacese). 



SPECIAL STUDIES. 



I. Determination of species of poplar, by means of 



winter buds. 

 II. Recognition of different species of willow by size, 

 habit, and other external. features. 



Note. — The identification of willows and poplars is attended with 

 some difficulty, requiring long practice and the exercise of critical judg- 

 ment ; but it is desirable that even beginners should observe how readily 

 the large-toothed aspen, Populns grandidentata, may be distinguished 

 from Populus tremuloides by its bud-scales, how Salix lucida is at 

 once recognized by its leaves, and how Salix alba and Salix nigra 

 are distinguishable from other species by their size and from each other 

 by their habit, even at a distance. Simple exercises of this sort may be 

 introduced occasionally with great advantage. 



