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, (CO 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 ceUs are found small chloroplasts composed 



