632 



SCIENCE 



[N. S. Vol. XXVII. No. 694 



periments with agar agar, where wheat seed- 

 lings are grown inside of glass tubes with 

 inside diameters less than that of an ordinary 

 lead pencil (6 to 8 mm.) and 3.3 cm. long; 

 three such tubes placed end to end, supported 

 on a glass rod with their ends separated 2 to 

 3 mm., thus forming a segmented tube to be 

 filled with transparent agar agar, solid when 

 cold, and standing in similar agar contained 

 in a glass vessel, the whole system arranged 

 to be revolved on a klinostat to neutralize the 

 directive efiect of gravity. When previously 

 germinated wheat plants are transplanted into 

 the agar inside one of these tubes before it 

 has solidified, and compelled to g^ow with its 

 roots thus circumscribed it is held that if 

 toxic excreta are developed they will become 

 so potent as to compel the roots, when they 

 reach a gap between two segments, to turn 

 from their course along the axis of the tube 

 and grow outward into the fresh uncontami- 

 nated agar of the outer vessel. It is assumed 

 that if more roots turn outward, the presence 

 of a toxic substance is demonstrated, and 

 further, that the toxic substance was excreted 

 by the roots and is a normal and necessary 

 function under field conditions. 



Plants were grown in free agar in large 

 numbers until the roots, by assumption, had 

 charged it with toxic substances ; such agar 

 was then remelted and filtered and used to fill 

 other tubes or to surround tubes containing 

 fresh agar, the contention being that if the 

 outside agar is more toxic than that inside the 

 tube a smaller number of roots would grow 

 outward into the poisoned agar. Just why 

 any should grow outward into the poisoned 

 agar is not made clear; probably it 

 is because those particular roots had 

 rendered the immediate contact agar more 

 toxic than that outside! But seriously, the 

 experiments would seem to be quite as con- 

 clusive a proof that the roots growing inside 

 the tube, or growing in the free agar, have 

 reduced the water content of the agar or its 

 soluble salt content and that the roots simply 

 turned one or the other way according as 

 available water or soluble salts are more 

 abundant. Our own observations have shown 

 that plant slips placed in water containing 



sugar, dextrine, agar agar in the condition de- 

 scribed by the Bureau of Soils, and even in 

 water holding suspended clay, wilt sooner or 

 become less turgid than check slips placed in 

 pure water, thus indicating that water is less 

 readily obtained under those conditions. It 

 is certainly to be expected that when as many 

 wheat roots grow under such cramped con- 

 ditions as are here under consideration, as are 

 reported in the bureau's experiments, there 

 must be developed a stress for water and it 

 seems just as rational and quite as certain that 

 the deflection of the roots may have been due 

 to this condition. The growing of large num- 

 bers of plants in free agar agar would cer- 

 tainly reduce the per cent, of water and the 

 melting of it over would reduce it still further. 

 As it is not said that strict quantitative meas- 

 ures were taken to secure absolute equality of 

 water and salt content between the inside and 

 outside agar, the results are subject to the 

 same intei'pretation as that suggested. These 

 ingenious experiments, therefore, can not be 

 seriously held to demonstrate that roots ex- 

 crete toxic substances, neither can it be held 

 that even if toxic substances were developed 

 as either normal or abnormal conditions the 

 deflection of the roots was due to them, and 

 there is nothing in the whole range of experi- 

 mental work covered by the three bulletins in 

 question which can be held to establish, or 

 even necessarily suggest, a probability of toxic 

 substances in soils which seriously affect their 

 productivity. 



The loose reasoning here referred to, and 

 characterizing the whole of Bulletin 40 and 

 indeed of the other two as well, appear, to the 

 writer, so out of accord with the planning and 

 execution of these particular experiments with 

 agar agar, when coupled with our personal 

 acquaintance with the one whose name appears 

 as senior author, that we are unable to feel 

 that either the language used or the conclu- 

 sions drawn are his. This I do know: It was 

 my great surprise and misfortune, after hav- 

 ing submitted manuscript for publication, to 

 find my own name on the printer's proof as 

 joint author of Bulletin 22, maintaining views 

 directly opposed to those we had submitted 

 and which had been laid aside, not to be pub- 



