LIFE HISTORY OF THE MALE FERN 63 
4, ENDODERMIS, a continuous layer of cells whose radial and 
inner walls are more thickened than the outer walls and which 
surrounds each bundle and binds it in place. 
Between the endodermis and the vascular bundle will be noted 
one or more layers of thin-walled PERIcycLE cells. In the regions 
of larger bundles, collenchyma tissue composed of thick-angled 
cells occurs between the endodermis and the two epidermal layers. 
5. Lower Epipermis of wavy-walled, flattened, chlorophyl- 
loid cells with thin cuticle and many stomata (breathing pores). 
Each Stoma is surrounded by a pair of crescent-shaped guard 
cells which regulate its opening and closing. The upper and 
lower epidermis are continuous around the laminar margin. 
CoMPARATIVE PuysioLoGy OF Root, STEM AND LEAF 
(FronpD).—The primary function of the roots of the Male Fern is 
that of ABsoRPTION of water with mineral salts in solution. The 
secondary function is that of Support for the stem, the tertiary, 
that of Srorinc Foopsturrs to tide the plant over the season when 
vegetative activities are lessened. Water is the most essential 
of all materials absorbed by vegetable organisms. It is found in 
the soil surrounding the soil particles with certain mineral salts 
dissolved in it. The delicate root-hairs with thin cellulose walls, 
protoplasmic lining and sap denser than the soil water, are firmly 
adherent to these particles. The soil water diffuses through 
these walls by osmosis and comes into relation with the outer 
plasma membrane or ectoplasm, a delicate protoplasmic membrane, 
which has the power of selecting what it wants and rejecting 
what it does not need. In this way only such solutes as are of 
value to the plant are admitted. The water with mineral salts 
in solution, once within the root-hair protoplast, is called “crude 
sap.” This passes through the hair into the cortical parenchyma 
cells which are in contact with the scalariform tracheids. It 
passes from one cortex cell to another by osmosis and, under con- 
siderable root pressure, is forced into the scalariform tubes of the 
xylem. Therein it is conveyed upward by root pressure through 
the tracheids of the stem bundles into those of the leaves and 
finally osmoses into the leaf parenchyma cells (mesophyll). 
Carbon dioxide (COz2), from the air, enters the leaf through 
the stomata. From the stomata it moves through the inter- 
