LIFE HISTORY OF THE MALE FERN 
39 
embedded in the mesophyll. The xylem portion of each bundle is 
nearest to the upper surface of the leaf and so the bundles approach 
the collateral type. 
4. Endodermis, a continuous layer of mesophyll cells which sur¬ 
rounds each bundle and binds it in place. 
5. Lower epidermis of wavy-walled, flattened, chlorophylloid 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 con¬ 
tinuous around the laminar margin. 
Comparative Physiology of Root, Stem and Leaf (Frond).— 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 storing food¬ 
stuffs 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 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 spiral ducts and scalariform tracheids. It passes 
from one cortex cell to another by osmosis and, under considerable 
root pressure, is forced into the spiral and 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, (C 0 2 ), from the air, enters the leaf through the 
stomata. From the stomata it moves through the intercellular-air- 
spaces to the mesophyll cells which line these, whence it is absorbed. 
Within the mesophyll cells are found small chloroplasts composed 
