138 STUDY OF COMMON PLANTS. 



1. The succession of nodes and internodes. Are there 



any branches ? 



2. The whorls of modified leaves arising at the nodes. 



How many leaves are there at each node? Are 

 they separate or united ? Do they diiTer in either 

 texture or color from the stem ? If so, how ? 



3. Surface, form, and structure of the stem. Cut a 



transverse section of an internode and examine 

 under a dissecting microscope. Is it solid or 

 hollow? Notice the openings, lacunae, and their 

 number and position. Are these constant in differ- 

 ent specimens? Is there any mechanical advantage 

 in such a disposition of material ? 

 Make an outline sketch of the section, using, if 

 necessary, a higher magnifying power. 



II. Study next the spike terminating the stem and 

 bearing the fructification. It will be seen that it is a 

 modified portion of the stem, showing a succession of nodes 

 and internodes, and exhibiting more or less perfectly the 

 same structural features as other parts of the stem. 



1. With a pair of fine forceps remove one or more of 



the leaves, here called scales, and examine them 

 carefully. Their study will be facilitated by 

 making transverse and longitudinal sections of the 

 spike, so as to expose the scales more fully. Are 

 they stalked or sessile ? Draw one in outline. 



2. Examine under a lens the spore-cases, sporangia, 



borne on the under surface of each scale. How 

 many are there ? What is their shape ? Make an 

 outline sketch. 



III. Remove carefully one of the sporangia, mount in 

 water, and examine with the compound microscope. Be 



