140 REPRESENTATIVE PLANTS 



free from each otlier or united into a net. Remove a small 

 portion of the epidermis from the upper and the lower sur- 

 faces, mount in water, and examine (Ip). Study the trans- 

 parent parts for stomates and guard cells. How do the 

 two epidermal layers differ ? Which epidermis has the 

 stomates ? What reason can you give for their absence in 

 the other epidermis ? Study a stomate carefully, and find 

 its shape, and the number, shape, and features of the guard 

 cells (Zp). 



Study a section of the fern pinnula to find the relation 

 of the epidermal layers, stomates, and mesophyll. Where 

 is the chlorophyll? 



Reproduction, the sori and contents. Examine fertile 

 leaves of the Boston, shield, spleenwort, and brake ferns 

 for brownish structures on their surface. On which surface 

 dD you find them? These structures are sort (sorus). 

 What relation to the veins ? How are they situated with 

 reference to the midrib of the lobe and to the margin? 

 Compare the sori of as many other ferns as you may have 

 access to, observing the difference in shape and size. The 

 sorus is often covered with a thin skin or flap, or leaf part 

 (indusium). What use may this have? How may it have 

 originated? Examine a sorus {l}^). Of what is it com- 

 posed? Try to isolate one of the structures (sporangia) 

 and study it carefully. Observe its form, the stalk or 

 pedicel (if present), and a peculiar partial ring of cells 

 {annidus). Try to see the sporangium from various points 

 of view. How does the position of the annulus vary? 

 How much of the sporangium wall does it embrace? Do 

 you find any opening in the wall? If the sporangium is 

 only partly grown, observe small irregularly triangular 

 or round objects through the partly transparent wall. 

 Those are the spores. Seek to discover the purpose of 

 the annulus. What would you say, from a study of the 

 spores, sporangia, and sori on a fern leaf, as to the total 



