Chap. 4 PLANTS PROVIDE FOR THEMSELVES AND THE ANIMALS 57 



dioxide and water unite to form glucose (CoHn-Oe), the simple sugar from 

 which all the organic compounds of plants and animals are eventually derived. 

 The chlorophyll itself is not used up and is evidently a catalyzer that hastens 

 other chemical processes. 



Green plants include the seed plants, and the mosses, ferns, the green algae, 

 and the lichens, many first named by Carolus Linnaeus in his two-name system 

 (Fig. 4.4) . As already noted, besides these there are other plants whose chloro- 

 phyll is blanketed with various colors, as in the deep red, yellow, or variegated 

 Coleiis often called foliage plants. The pigment of red and brown seaweeds also 

 effectively clothes the chlorophyll as does the brown cloak of the microscopic 

 diatoms of fresh and salt waters. Although the process of food-making in these 

 plants is not clearly worked out, it is certain that pigments other than green 

 ones take an important share in it. One investigator has observed that in red 

 seaweeds the light absorbed by red pigments is more efficient in photosynthesis 

 than that absorbed by the green of chlorophyll. The food product in blue-green 

 algae, for example, is not glucose but glycogen which is also found in fungi 

 (bacteria, molds, mushrooms, and rusts) and in the tissues of animals. The 

 tons of rockweed washed by the breakers on many headlands press home the 

 estimate that "90 per cent of the photosynthesis on earth is carried out, not 

 by green land plants, but by the multicolored sea algae" (Fig. 4.5). 



Studies of Photosynthesis. In 1772 Joseph Priestley discovered that a plant 

 produced oxygen. He piped air into a glass jar from another jar in which a 

 mint plant was growing. Then he put a lighted candle in the empty jar and the 

 candle, being well supplied with oxygen from the plant, went on burning. Later 

 he took the candle out and put a mouse into the same jar. The mouse breathed 

 comfortably and Priestley wrote of it, "nor was it at all inconvenient to a 

 mouse which I put into it" (Fig. 4.6). In 1779 Jan Ingenhousz, a court phy- 

 sician to Empress Maria of Austria, observed that plants "corrected the bad 

 air" in which they were growing. He wrote of his observations, "I found that 

 this operation of the plants is more or less brisk in proportion to the clearness 

 of the day and the exposition of the plants." Julius R. von Mayer, who formu- 

 lated the principle of conservation of energy, first stated in 1845 the physical 

 function of photosynthesis as the conversion of light energy into chemical 

 energy. Photosynthesis is a subject of joint chemical and biological inquiry in 

 which new dscoveries are made from month to month, and sunlight has created 

 sugar from carbon dioxide and water. 



Organization of a Green Plant 



Essential Needs. Plants are light-seeking, light-directed organisms. They 

 have four essential needs, light, air, water, and certain minerals. The sun sheds 

 its energy in light and heat upon the earth. It creates currents in the water, 

 winds in the air, quickens the activity of water molecules that scatter as vapor. 



