CAPSELLA BURSA-PASTORIS. 225 



7. Draw the section. 



Make a longitudinal section through a branch and leaf- 

 bearing node, and note 



8. The three regions, as well as 



9. Their relation to the leaf and branch. 

 10. Illustrate with diagram. 



D. THE LEAF. Note 



1. Two sorts of leaves : 



a. Root-leaves, clustered at the base of the stem. 



b. Stem-leaves. 



2. Leaf arrangement (p/iy/lotaxy). Observe that an imagi- 

 nary line connecting the insertions of successive stem 

 leaves is a spiral. Discover the number of times the 

 spiral encircles the stem, and the number of leaves it 

 passes, before reaching a leaf standing directly over the 

 first. 3 



3. Leaf parts ; in the root-leaves a blade and leaf-stalk or 

 petiole, in the stem-leaves simply a sessile blade. 



4. Leaf shapes and sizes, the great variety. Draw a series 

 of the most characteristic. 



5. Leaf surfaces j differences between the upper and 

 lower. Notice 



a. Simple hairs. 



b. Stellate hairs. 



6. Distribution of the veins, and their relation to the teeth. 



7. The uncoiling of the spiral threads, when the leaves are 

 broken by careful stretching. 



3 The student may find it easier to substitute a thread for the imagi- 

 nary line, and must also allow for any twisting of the stem. 



