INTERMEDIATE ORGANISMS 



1ST 



drate foods from these substances are not yet clear, the essential facts 

 are well established. The carbon dioxide and water are partially or com- 

 pletely reduced to their elements, which immediately recombine to form 

 a monosaccharide sugar (probably dextrose) with the freeing of oxygen. 

 These two processes are represented by the reaction 6CO 5 -|-6H 2 O 

 C 6 H 12 O 6 -|-6O2. The oxygen is given off into the atmosphere through 

 the cell wall. The sugar is the primary food of the plant, being the 

 principal material used in the synthesis of other foods and in the pro- 

 cesses of metabolism. When 

 it is produced in excess of the 

 immediate requirements a fur- 

 ther reaction takes place by 

 which some of the water is 

 eliminated and the sugar is 

 "condensed" into starch ; this 

 reaction is n(C 6 H 12 O ) = 

 (C 6 H 10 5 )n+n(H 2 0). 



"This starch is deposited in 

 the chloroplast as granules or 

 "starch grains" and forms a re- 

 serve food supply for the cell ; 

 in green plants kept in dark- 

 ness the starch grains soon 

 disappear ~ and reappear only 

 after the plant has again been 

 in the light for a considerable 

 period of time. In some plants, 

 e. g., Vaucheria (Fig. 86), the 

 excess food is stored in the 

 form of a fat or oil, but it is 

 probable that here also the first 

 food formed is a sugar. 



"This process by which car- 

 bohydrates are manufactured 

 in green plants is called photo- 

 synthesis; its essential fea- 

 tures are summarized as fol- 

 lows: The materials used are 

 carbon dioxide and water; the 

 energy is obtained from sun- 

 light absorbed by chlorophyl ; 

 the chloroplast by the use of 

 this energy brings about a 

 chemical synthesis of the materials, resulting in the freeing of oxygen 



Fig. 86. 



I. Asexual Reproduction of the Green Felt 



(Vaucheria). 



A, formation and discharge of the large, many- 

 ciliate zoospore from the terminal sporangium ; B, 

 the zoospore showing the ciliated surface ; C, sec- 

 tion through the surface of the zoospore showing the 

 pairs of cilia above the nuclei and the layer of plastids 

 beneath ; D, germination of zoospore ; E, young plant 

 of Vaucheria, the two filaments having arisen at op- 

 posite ends of the zoospore, one having developed an 

 organ of attachment or holdfast h ; F, a group of 

 plastids, the lower in process of division. (A, B, 

 after Gotz ; C, after Strasburger ; D, E, after Sachs. ) 



II. Sexual Reproduction of the Green Felt 



(Vaucheria). 



A, Vaucheria sessilia ; o, oogonium ; a, antheridi- 

 um ; 08, the thick-walled oospore, and beside it an 

 empty antheridium ; B, Vaucheria geminata, a short 

 lateral branch developing a cluster of oogonia and a 

 later stage with mature oogonia o and empty an- 

 theridium a ; C, sperms ; D, germinating oospore. 

 (From Bergen & Davis "Principles of Botany" by 

 permission of Ginn & Co., Publishers. C, after 

 Woronin ; D, after Sachs. ) 



