Problems of Plant Physiology 51 



with the chemical side of the question and are of such great importance 

 that they are indispensable to an understanding of the subject. But 

 the function of chloroplasts interests us most. Among the questions 

 are the formation of starch and other substances ; the first-formed 

 products; is the same course always followed in sugar production; and 

 the chemistry of pigments. Can oil produce starch or vice versa in the 

 chloroplast independently of the cytoplasm? Are glucosides direct prod- 

 ucts of photosynthesis? Further studies should be made on the retard- 

 ing influence of higher carbon dioxide percentages and on the more 

 or less complete loss of photosynthetic power by normal chloroplasts. 

 Is the protoplasm of heliophobic plants more sensitive to light than the 

 chloroplast? (1, Bd. I, p. 285.) 



The evolution of oxygen from water plants directed the attention 

 of Ingenhousz to the photosynthetic processes in green plants and his 

 work in connection with that of Senebier and De Saussure constitutes 

 one of the most important scientific discoveries. Iron is necessary to 

 chlorophyll formation, but the action of iron and alum in causing the 

 reddish flowers of Hydrangia to become blue is uncertain (1, Bd. I, p. 

 421). Chemical reactions often occur with great velocity. So w^e may 

 have an immediate cessation or recommencement of oxygen evolution 

 in green plants as shown by the extremely sensitive bacteria method. 

 In light, starch (1, Bd. I, p. .303) is produced in five minutes in con- 

 siderable amount in Spirogyra which previously was starchless (82). 

 Detmer has shown that the iodine reaction of starch can not be obtained 

 in distilled water (83). No means of stabilizing this reaction is known. 

 We have a great many chemical changes occurring in tiny green cells 

 whose total volume often does not equal 0.1 cubic millimeter. Since 

 the air contains only .03 to .04 per cent of carbon dioxide the work 

 necessary on the part of the green plant to make its food will be 

 easily understood. 



Light we know is necessaiy for chlorophyll action, therefore it is 

 not surprising that moonlight which is about 1/600000 the strength of 

 sunlight would prevent the handling of CO- and even with light of 

 0.1 to 0.025 the strength of sunlight respiration and photosynthesis 

 about balance (1, Bd. I, p. 323). Plants in dwellings often suff"er 

 from deficient light since at 0.5 meter from a window the plant gets 

 only 0.3 and at a distance of two meters only 0.08 of the light it would 

 get in the open sunlight (1, Bd. I, p. 323). When the sunlight falls 

 on a thin green leaf most of the energy is usually absorbed so that the 

 light which passes through would not cause the formation of starch 

 nor an evolution of gas (1, Bd. I, p. 329). Copper beeches due to their 

 color and light interference grow more slowly than vividly green species, 

 other conditions being equal (84). An oleander leaf will produce per 

 square meter in sunlight about 0.000535 gram of starch in one second, 

 obtaining thereby energy equivalent to 2.2 caloric units, which is less 

 than one per cent of the energy of the sunlight (84). Under good 

 conditions other plants such as the pumpkin may produce in 15 hours 

 25 grams of starch per square meter (85) which necessitates the removal 

 of the carbon dioxide from 50 cubic meters of air. The quantitative 



