142 STUDY OF COMMON PLANTS. 



arise, whether from the lower (ventral), or upper (dorsal) 

 side of the stem. Where their ends come in -contact with 

 the soil, roots are produced. Observe their peculiar mode 

 of branching, unusual for roots. 



Fructiflcation . 



The fertile branches are not particularly conspicuous and 

 may be overlooked; they are readily recognized, however, 

 by their rigid, erect habit and quadrangular outline, in 

 contrast with the flattened and spreading sterile branches. 



I. Notice the form and arrangement of the leaves. 

 How do they differ from those of other parts of the plant ? 



II. The spore-cases, sporangia, arise singly in the axils 

 of the leaves. They are of two kinds, microsporangia in 

 the axils of the upper leaves, and macrosporangia, few in 

 number, in the axils of the lower leaves of the fertile 

 branch. Examine different specimens, under a good lens, 

 until you are satisfied as to the position of the two kinds 

 of sporangia and their external differences. 



III. With a pair of fine forceps remove the upper part 

 of a fertile branch with its microsporangia. Dissect care- 

 fully on a slide, and examine with the low power of the 

 compound microscope. Compare the sporangia as they lie 

 in various positions and notice 



1. The exact relation of the sporangium to the stem 



and leaf, and whether it is stalked or sessile. 



2. Its form and mode of dehiscence. 



Note. — The cause of the opening of the sporangium may not 

 be obvious, but there is no difficulty in finding the line of dehis- 

 cence and observing the escape of the spores. 



3. The structure of the sporangium wall. 



4. The spores, set free in great numbers when the spo- 



