144 TYPE STUDIES 



7. Study the jointed structure of the branches, the sheaths, 

 the method of branching. AVhat part of the plant per- 

 forms the work of photosynthesis ? 



Draw a portion of the vegetative shoot to ilhistrate the 

 above points. 



B. The cone and its scales, or sporophylls. Study from pre- 

 served material. 



1. Draw a cone in detail (if not drawn under A), showing 

 the arrangement of the hexagonal scales in circles around 

 the stem. Why should their form be six-sided ? Com- 

 pare the circles of scales with the nodes or joints of the 

 stem bearing circles of leaves forming sheaths. 



2. Cut off several scales, noting the central stalk bearing the 

 six-sided plate and the sac-like sporangia hanging down 

 from the plate. Draw two side views of the scales as 

 seen somewhat obliquely from above and below. The 

 scales are highly specialized spore leaves, or sporophylls. 

 What are some of the reasons why they should be so 

 considered ? 



C. The sporangiuni and its spores. Split a sporangium open 

 with the point of a needle. Examine under h.p. Note : 



1. The spores, each bearing four filamentous elaters, devel- 

 oped from four segments of the outer spore wall, which 

 separate from one another and the spore except at one 

 point. 



2. Allow the spores to become dry and note the position of 

 the elaters. Draw. 



3. Breathe gently on the dry spores or moisten them and 

 observe the behavior of the elaters. Draw various spores. 



\. Study the structure of the sporangium wall, the cells of 

 which are irregularly thickened. Draw a portion under 

 h.p. How does the sporangium wall rupture ? What 

 mechanical forces are at work to make it split open ? 



D. The cell structure or histologi/ of the stem. Cut sections 

 across the stem between the nodes. Observe under l.p. the 



