RESPIRATION AND OXYGEN. 23 



Chambers (1912 : 203) summarizes his results upon the relation 

 of algse to gases as follows: 



"There is an intimate and mutual relation between the algae and submerged 

 aquatics in a body of water and the gases dissolved in that water. They 

 fluctuate together. Air, or its constituents, oxygen and CO 2 , are as essential 

 to water-plants as water is to land-plants, and equally difficult to secure. 

 Warm and stagnant water is poorer in these essentials than colder water 

 gently agitated by wind or currents. Currents are especially beneficial to 

 attached plants by renewing or removing these gases. Some species demand 

 more aeration than others. Some species are more tolerant of stagnant 

 water than others. Filamentous forms with large cells and thin outer walls 

 are best adapted to stagnant waters. Such forms predominate in warm, 

 tropical fresh waters, which are poorly aerated. Stagnant water, on account 

 of the large amount of CO 2 and the small amount of oxygen, favors the forma- 

 tion of colonies and filaments rather than of free individual cells. Colonies 

 and filamentous forms may be produced artificially with some plants by in- 

 creasing the amount of C0 2 or diminishing the amount of oxygen in the 

 culture solutions. Narrow, much-branched filaments are adapted to and 

 produced by poorly aerated waters. Aeration or abundance of oxygen 

 apparently favors the formation of chlorophyll; and algse are brighter green 

 when well aerated. The periodicity of spore formation is not readily influ- 

 enced by aeration or gas content of the water. It seems to be more a matter 

 of heredity." 



Hunter (1912 : 183) has grown plants in five different types of 

 soil as follows: (1) soil with small lumps, loose; (2) soil fine, loose; 

 (3) soil fine, firm below with loose surface; (4) soil fine, firm; (5) 

 soil fine, hard. Seeds of Helianthus, Pisum sativum, Triticum, and 

 Lepidium sativum were sown in the pots with a more or less equal 

 water-content. The plants made very different growths in the sev- 

 eral soils. The roots were longest in pot No. 1 and shortest in No. 5. 

 The plants in the latter were small and the roots were unable to 

 penetrate the soil much below the surface. The plants in the loose 

 fine soil had the largest leaves and the best developed root-system of 

 the series. The differences in growth were attributed to variations 

 in the amount and movement of the soil-air. This was supported 

 by determining the resistance offered to the movement of air through 

 the various soils. The loosest soil was taken as unity and the rela- 

 tive restistance of the other four was as 2, 17, 42, and 310. Further 

 proof was obtained by planting badly developed seedlings with weak 

 stems and curled leaves in soil through which 15 liters of air were 

 drawn each day for 3 weeks. In 2 or 3 days the seedlings sub- 

 jected to the air-currents became more robust and the stems 

 stronger, while the leaves grew rapidly and became much larger 

 than those of the control plants. By comparative water-cultures, 

 in which one series was not aerated at all, while another had a con- 

 tinuous current of air bubbling through, Hall, Brenchley, and Under- 

 wood (1914 : 278) have shown that barley and lupine in the aerated 



