THE FERN 99 



zation, between plants and animals, as well as to demon- 

 strate the contrasts of structure and their relations to the 

 markedly different functions to be performed. 



I. Leaf or Frond. 



1. The stalk or stipe bears the expanded, foliaceous part 

 with its numerous lobes, pinnae, which are further subdivided 

 into ultimate leaflets, pinnules. Note whether there are, 

 on any part of the frond, hair-like elements, trichomes. 



2. Midrib and veins are special structures forming a sort 

 of framework of the leaf. Are midrib and veins derived 

 from the stalk and connected with it? Do they sustain 

 any relation to the lobings of the leaf? Not only do these 

 form a structural framework, they are also paths for the 

 movements of liquids. 



3. Histology of the Leaf. From portions of the leaf re- 

 move bits of the epidermis and examine with both low and 

 high power and study the structure. Are cells present? 

 Observe the shape, structure, contents. Compare the 

 epidermis from both sides of a leaflet and note likenesses and 

 differences. Look for minute pores, stomata, and note upon 

 which side of the leaflet they occur. They are the so- 

 called breathing pores, and relate to the functions of trans- 

 piration and respiration. Sketch cells of the epidermis. 



II. Rhizome. 



Study sections of the rhizome and note the varied aspects 

 of different regions, which indicate the several tissues, or 

 tissue systems, of the rhizome. On the outside is the cortex, 

 made of an outer layer of epidermis, lifeless and protective, 

 and beneath this a subepidermis whose cell walls are hard 

 and woody, but which contain living protoplasm. 



