40 PHARMACEUTICAL BOTANY 



of protoplasm and chlorophyll. The kinetic energy of the sun's rays 

 is absorbed by the chlorophyll which j's thus energized to break up 

 the CO 2 and H 2 O into their component elements C,H and O, and 

 rearrange them in such a way as to ultimately form sugar or starch. 

 This process is called photosynthesis. According to von Baeyer, 

 CO 2 is split into C and O 2 , the C being retained, the O 2 given off. 

 The nascent C is linked with H 2 O to form CH 2 O (formic-aldehyde) ; 

 six molecules of this are then united to form grape sugar (C 6 Hi 2 O 6 ). 

 The formation of starch may be expressed by the following equation : 

 6C0 2 + sH 2 = C 6 Hi O 5 + 6O 2 . A portion of the grape sugar is 

 removed from solution by the chloroplast and converted into starch 

 which is stored up within it; another portion is used to nourish the 

 protoplasm of the cell. But the greater portion of sugar manu- 

 factured descends in solution through the phloem cells of the bundles 

 of the veins, mid-rib and stipe to the stem or roots, where it is re- 

 moved from solution by the action of the leucoplasts which convert 

 it into reserve starch. Sugar and starch, however, are not the only 

 food materials manufactured in the leaf. Proteins are likewise 

 formed. These are composed of carbon, hydrogen, oxygen, nitrogen, 

 sulphur and sometimes phosphorus. They are formed from grape 

 sugar with the addition of nitrogen and the other elements by the 

 living protoplasm. The source of nitrogen, sulphur and phos- 

 phorus is the mineral salts which are found in the crude sap. These 

 proteins descend through the sieve tubes of the veins, midrib and 

 petiole to the stem and roots, nourishing all of these parts with protein 

 material. 



Gross Structure and Histology of the Sori and Sporangia. The 

 sporangia or spore cases are found clustered together in circular 

 groups on the under surface of the pinnules nearer the mid- vein than 

 the margin. Each group of sporangia is covered with a membranous 

 expansion of the epidermis called the indusium. The whole is called 

 a sorus (Fig. 12) (pi. sori) and contains many sporangia. Each 

 sporangium is composed of: (a) the stalk of considerable length and 

 usually comprising three rows of cells, outgrowths of the epidermis of 

 the pinnule; and (b) the head, sub-globular and hollow, consisting for 

 the most part of a covering of thin walled, flattened cells, within 



