RESPIRATION OF PLANTS 93 



Such a coincidence of optimum temperatures in so widely 

 differing representatives of the organic world is certainly basically 

 significant and serves as an indicator of the profound unity of 

 the fundamental properties of their protoplasm. 



Respiration is greatly influenced by the degree of swelling of 

 the colloids of the protoplasm, increasing with the degree of 

 their saturation with water. Dry seeds, containing only 10 to 

 12 per cent of hygroscopic water, do not display noticeable signs 

 of vital activity. The well-known observations of Kolkwitz 

 have shown that 1 kg. of dry seeds of barley hberated only 0.3 to 

 0.4 mg. of carbon dioxide per 24 hr. A small increase in the 

 water content up to 14 or 15 per cent is sufficient to increase 

 respiration 3 to 4 times, i.e., up to 1.3 to 1.5 mg. of CO2 per 24 hr. 

 With further swelling, respiration increases very rapidly, and at 

 33 per cent water it reaches 2 g. per kilogram, i.e., it increases 

 over 10,000 times. With the beginning of germination, it 

 increases still more. Similar data have been obtained for mosses 

 and hchens. These plants on desiccation go into a state of 

 inactivity but are capable of reviving after being moistened. 

 A similar gradual slowing down of respiration may be observed 

 in ripening seeds in connection with their desiccation. 



The amount of material available for respiration in the cell 

 also greatly affects the intensity of the process. As has been 

 seen, this material is represented chiefly by sugars and other 

 carbohydrates. The intensity of respiration is therefore rather 

 closely connected with the presence and influx of carbohydrates 

 and is considerably diminished in starving organs and cells. 

 This explains the close connection between the respiration of 

 leafy organs and their illumination, established by Borodin 

 (1876). When kept in darkness, their respiration decreases 

 gradually with the exhaustion of carbohydrates. After exposure 

 to light and a renewal of the carbohydrate reserves, it increases 

 rapidly. It has not been possible until recently to test the direct 

 influence of fight on the respiration of fiving celJs. Recent 

 experiments indicate that respiration is at the same rate, whether 

 the plant is in light or in darkness, if other conditions are kept 

 the same. An excessive illumination may cause an increase in 

 temperature that will correspondingly affect respiration; on the 

 other hand, it may affect the protoplasm injuriously, thus 

 involving a decrease in respiration. 



