I] 



STRUCTURE OF THE SPOROPHYTE 



3 



which serve various purposes in different parts. Thus in the root they may 

 be absorbent, while on the other hand they transmit the fluids absorbed to 

 the conducting system. In the stem they may serve the purpose of storage 

 of reserve materials, while in the leaf the parenchyma carries on the function 

 of photo-synthesis, together with the passing on of the supply thus acquired 

 to the conducting system. The parts exposed to the air are covered by an 





T^a^v 



Fig. 2. Dryopteris Filix-mas, Rich. Fertile leaf about one-sixth 

 natural size, the lower part with the under surface exposed. To 

 the left a single fertile segment, bearing kidney-shaped sori, en- 

 larged about seven times. (After Luerssen.) 



epidermal layer with a cuticularised external wall, which prevents the in- 

 discriminate loss of water b}' surface-evaporation. But the epidermis is 

 perforated by numerous stomata the mobile guard-cells of which according 

 to circumstances can control the width of the pores leading to the ventilating 

 spaces within. Finally, there are also firm brown resistant tissues disposed 

 sometimes near the outer surface, as in the stem and leaf-stalk: sometimes 



