1 68 SUNFLOWER. 



LABORATORY WORK. 



GROSS STRUCTURE. 1 



I. THE PLANT BODY. Observe: 



1. General arrangement of parts, especially: 



a. Number of leaves. 



b. Size of leaves and length of petioles. 



c. Arrangement of leaves on the stem in order to secure 

 proper exposure to light. 



d. The changes throughout the day in position of the tip 

 of a plant. What function is served by the change? 



2. The stem. Observe: 



a. The supporting strength. 



b. The hairs of the surface. 



c. In a transverse section observe: 



i. The central pith tissue, 

 ii. The strengthening tissue. 



3. The leaf. By means of surface mounts of the epidermis 

 and cross-sections of the leaf observe: 



a. The epidermal hairs; their abundance. 



b. The number and distribution of stomata as compared 

 with those of leaves already studied. 



c. The thickness of the cuticle, and the epidermal protec- 

 tion furnished to the stomata. 



d. Make drawings illustrating any structures of this leaf 

 not seen previously. 



1 In Helianthus as well as in the entire family Compositae the detailed 

 structures of the stem, leaf, and roots, and those that have to do with 

 the embryo-sac, fertilization, and seed formation, are essentially like 

 those already examined in other Angiosperms. Consequently the out- 

 line does not provide for work in these parts. The composite inflores- 

 cence, however, offers certain peculiar advantages for study of progres- 

 sive stages in the development of floral structures. 



