30 SCIENCE PROGRESS 



aeration by means of potsherds and sand. The results showed 

 an increased yield up to 40 percent., and the writer points out 

 the importance of aeration in irrigation lands where the caking 

 of soil is so prevalent. Experiments on tree seedlings by Hole 

 (Agr. J. India, 191 8, 13, 430-440) showed that in water culture 

 the water alone is not harmful, and that even in sand culture 

 no ill effects result from root submergence if the water used is 

 aerated. In water culture 500 mg. of CO2 per litre is sufficient 

 to kill roots. Howard also considers soil aeration to be an 

 important factor in disease resistance {Ann. App. Biol., 192 1, 

 7, 373-389), and is of the opinion that the destruction or 

 asphyxiation of the deeper roots by bad aeration, e.g. during 

 the wet season, predisposes the plant to disease as the result 

 of the reduction of root activity. The wilt of Java indigo, rust 

 of wheat and linseed, and red rot of sugar cane are mentioned 

 in this connection. 



Stiles and Jorgensen (New Phytologist, 191 7, 16, 1 81-197) 

 found barley and balsam sensitive to aeration in water culture, 

 and their results with buckwheat confirm the statement of 

 Free (above) that aeration in water culture has no difference 

 on the growth rate. 



Bergman, in a laboratory study of the ecological significance 

 of soil aeration [Ann. Bot. 1920, 34, 13-33), has recorded some 

 important results. Pot cultures were set up, using a variety of 

 plants from both dry land and swamp habitats. In the case 

 of land plants, the submergence of the roots in water invariably 

 resulted in wilting, death of leaves, and decrease of growth, 

 irrespective of whether the plants were growing in soil, peat, or 

 sphagnum. Examination of the root system showed that the 

 roots, except those near the surface, had died, and any roots 

 developed after submergence were found to have originated 

 near the surface, and were markedly less extensive than in the 

 controls. Day aeration by means of algae was found to have a 

 palliative effect on plants with roots submerged. Transpira- 

 tion measurements showed, as was to be expected, that sub- 

 mergence was followed by a decreased transpiration rate, 

 following upon the inability of the roots to continue their 

 absorption functions. On the other hand, plants from a swamp 

 habitat were found to suffer when grown in moist soil, root 

 submergence being apparently necessary for the proper develop- 

 ment and functioning of the root system. The difference 

 between the behaviour of these two types of plants is probably 

 to be found rather in morphological than in physiological 

 peculiarities. There is no evidence that hydrophytes generally 

 have a smaller oxygen consumption than mesophytes, but, on 

 the contrary, it appears that the hydrophyte by virtue of the 

 extent of its internal aerating system is able to effect the 



