284 



SCIENCE 



[Vol. LVI, No. 144.5 



ramify far beyond the depth of tillage (12 to 

 20 cm.) and their studies lead to the convic- 

 tion that much of the soil water and solutes 

 entering the plant during its later growth 

 stages must come from the greater depths. 

 This appears to be at variance with statements 

 in the prevailing text-books, as the authors re- 

 mark, but of course the discussion of root 

 activities is still necessarily very superficial 

 in such treatises. It seems probable that, with 

 increasing age of the plant, the region of great- 

 est absorption is gradually transferred to the 

 deeper soil layers. In almost every case of 

 actual excavation, the total root development 

 below the region of tillage was found to be as 

 great as, and usually much greater than, that 

 within the tilled region. To gain some quanti- 

 tative information regarding absorption from 

 the different soil layers, some ingenious ex- 

 periments were carried out. The methods de- 

 vised for this experimental study of absorp- 

 tion, together with the results secured, con- 

 stitute the most valuable part of this book, 

 and they should furnish an added impetus 

 toward a physiological phase of root ecology, 

 which is much needed and which seems about 

 to be developed from several points of view. 



Vertical sheet metal cylinders were em- 

 ployed as soil containers, large enough to allow 

 complete development of the plants. The moist 

 soil was placed in these, consecutive horizon- 

 tal layers 15 or 30 em. thick, separated by hori- 

 zontal wax partitions that prevented move- 

 ment of soil solution between adjacent layers 

 but did not hinder root penetration. Sodium 

 nitrate was added to some of the layers. 

 Several kinds of controls were also employed. 

 Rain was practically excluded. Oats, barley, 

 potato, maize and two native grasses were 

 studied, at various stages of their develop- 

 ment, determinations 'being made of the loss 

 of water and of nitrate from the several soil 

 layers. 



The amounts of water removed from the 

 different soil layers were closely related to the 

 frequency of roots, and absorption occurred 

 from all layers occupied by the root systems. 

 Maize absorbed large quantities from the third 

 and fourth 30-cm. soil layer (counting from 

 the top of the cylinder), and smaller quanti- 



ties from the fifth. Potato absorbed to a depth 

 of 75 cm., approximately the lower limit of 

 the root system. Similarly, nitrate was 

 markedly absorbed from the deeper occupied 

 layers; maize removed 203, 140 and 118 parts 

 per million from the third, fourth and fifth 

 30-em. layer, respectively. 



While the quantitative data are not ex- 

 pressed in terms such as would render them 

 most valuable from all points of view (the 

 authors use parts per million for nitrate 

 measurements and percentage data for water 

 measurements, both apparently based on the 

 dry weight of the soil), yet they furnish con- 

 vincing evidence that roots absorb water and 

 nitrate at whatever depths the roots occur in 

 the soil. This is quite in accord with what 

 should be expected from our knowledge of the 

 molecular physics of root absorption. 



When a root system advanced into a soil 

 layer to which nitrate had been added it de- 

 veloped more profusely than would have been 

 the case without the extra nitrate, and this 

 stimulation of branch development in the fer- 

 tilized soil was accompanied by a correspond- 

 ing retardation in the farther advance into 

 the next layer below. Fi'om this observation 

 it is suggested that, in field practice, the pres- 

 ence of added fertilizer salts in the super- 

 ficial soil layers may hinder the development 

 of roots into the deeper-lying soil, with possible 

 resulting crop failure in ease of a subsequent 

 serious lack of water in the surface layers. 



As a minor detail, it is regrettable that the 

 metric system of measurements of distance 

 seems not yet to have been appreciated by the 

 authors, though weights are expressed in grams 

 instead of ounces. 



From my own point of view, the authors' 

 presentation might have been improved con- 

 siderably by a more thorough digestion of the 

 results, with less space devoted to unessential 

 details and more given to the fundamental 

 considerations. There is evident a noticeable 

 tendency toward "publishing the note-book." 

 The general headings of the tables, and the 

 column headings, might have been made much 

 clearer. A well-made summary of the 

 descriptive portion of the book would have 

 rendered it much more valuable and far-reach- 



