RESPIRATION AND OXYGEN. 99 



watering (206), and deep planting of trees and seeds. The relation 

 of aeration to growth and the treatment of soils to promote it are 

 considered at considerable length in his ''Popular Treatise on the 

 Physiology of Plants" (1895 : 61), under the headings, "How can the 

 soil best meet the requirements of the roots for air?" "How can we 

 improve our fields so as to obtain the best possible crops?" "How is 

 the nutrition of pot-plants effected?" and "How do ordinary roots 

 obtain their necessary supply of air?" 



Sorauer stated that plants without access of oxygen gradually die. 

 When the living cells can absorb no more oxygen their functions un- 

 dergo a change of direction; later they pass into a state of rigidity, 

 in which movement of the protoplasm ceases, sensibihty to stimuli 

 is lost, and growth stops. However, the plants do not die immedi- 

 ately; they exhale carbon dioxid for a long time and can resume their 

 functions upon renewed access of oxygen, even after apparent death. 

 Sour soil is immediately recognized by its peculiar odor and a wholly 

 different process of decomposition of the organic matter occurs in it. 

 There probably arise acid combinations in the little-known series of 

 humus compounds, in addition to the free acids formed. If iron is 

 present, the harmless ferric salts may be reduced to the ferrous ones, 

 since perceptible lack of oxygen must result from the filling-up of the 

 soil spaces with water. Water filled with carbon dioxid derived from 

 the root secretion as well as from the decomposition of organic mat- 

 ter alone suffices to kill plants after protracted action. 



Vonhausen (1877 : 724) placed a clay drain-tube in the middle of 

 a third of the length of a seed-bed sown with seeds of Platanus. 

 The ends of the tube led out to the surface of the soil. At first the 

 non-aerated portion showed no difference, but from the beginning of 

 August the growth in the aerated portion was much greater both in 

 height and in luxuriance. It was suggested that a similar method 

 of aeration could be used in all nursery and seed-beds, and that it 

 might be employed in vegetable gardening as well. 



Bohm (1881) found an example of disease due to faulty aeration in 

 the case of dying Ailanthus that had been planted too deeply in the 

 Ringstrasse in Vienna. These trees had been diminishing in growth 

 for a number of years, as the annual rings formed soon after planting 

 were often more than 3 mm. wide, while those of the years preceding 

 the death of the tree were but 0.5 mm. At the death of the trees the 

 earth of the root-ball was so injurious that seeds of different plants 

 quickly decayed when placed in it. The seeds readily developed, 

 however, after the earth was repeatedly soaked with water and ex- 

 posed in a thin layer to the action of the summer sun. 



Wollny (1889^: 379) stated that in general the most important rule 

 for agricultural practice was to increase the access of atmospheric 

 air to the soil in the most complete manner possible. Soil in the 

 powdery condition contains less air than a crumbly one, and the dif- 



