30 EXPERIMENT STATION RECORD. [Vol. 43 



Grassinjj: over half of a iilaiilalioii of standard trees of a strong-growing 

 apple variety 25 yeai-s old reduced the crops 5 per cent during tlie tirst season 

 and 50 to 90 per cent during the second. The removal of tlie grass hefore the 

 third s(nison resulted in no detinite recovery during that season hy these trees, 

 which appeared to he permanently injured. 



lu case of sucli plants as mustard, tobacco, and tomato, where the experi- 

 ments were conducted in pots, the surface crop was grown in a circular per- 

 forated tray, resting on the surface of the soil surrounding the plants. Besides 

 grass, numerous other plants were grown as surface crops. The large number 

 of instances with no exceptions supports the view that tlie deleterious effect 

 of one plant on another is general and probably more marked in case of plants 

 of the same kind, plants thus in all probability being affected by their own 

 toxins., 



ISo toxin has been identified, but the toxic agent appears to be easily oxidiz- 

 able and after oxidation (wliich may be complete after 24 hours or may in 

 certain cases practically or entirely keep pace with its production) it acts 

 as a plant food. Apparently there is no exudation of toxic matter from the 

 roots, and it is regarded as more likely that the toxic matter is some product 

 of growth. A certain amount of recovery seems to occur in case of soft-wooded 

 plants if the injury is not carried too far. The toxic action appeared to have 

 no connection with carbon dioxid produced by surface growth, and was not 

 counteracted by lime. Some results are not yet explained by previous experi- 

 mentation. 



In a study of the effects of plants on each other, it was found with undi- 

 vided pots that the total amount of plant growth produced, wlien the mass of 

 soil available is below a certain limit, is independent of the number of plants 

 grown ; that is, the total weight of individual plants is proportional to the area 

 occupied by them. Root interference does not apply here and the same results 

 are obtained in divided or in undivided pots. This was true only of plants of 

 the same age. Older plants, where root interference is allowed, flourish at 

 the expense of the younger ones, which may be reduced fully one-half as re- 

 gards their normal growth. With mustard, a difference of four days in the 

 ages of the plants present was sufficient to reduce the whole crop 20 per cent, 

 this fact supposedly bearing directly on the advisability in preparing seed beds 

 of employing seeds having a uniform germination period. This is also sup- 

 posed to indicate the futility of attempting to fill up vacancies in a plantation 

 by means of replants. 



Interference of the portions above ground has but little effect on the amount 

 of growth, but considerable effect on its character as being taller and more 

 slender. Outside rows were stronger than inside rows. Explanations attribut- 

 ing this to the extra food supply are regarded as untenable. 



Removal of the toxins from the soil by means of leaching with water has been 

 found to result in greatly increased growth, though other factors are insep- 

 arably involved. Other observations and deductions are given. 



A comparative account of the root-nodules of the Leguminosae, E. R. 

 Spbatt (Ann. But. [London], 33 {1919), No. 130, pp. 189-199, pi. 1, figs. 5).— 

 This discussion includes, besides the legumes, other plants named which re- 

 spond by the production of root nodules to attacks by Bacillus radicicola and 

 which also actively assimilate nitrogen. 



Root tubercles in legumes are said to be exogenous in origin, those of non- 

 legumes being modified lateral roots. B. radicicola is connected with the assim- 

 ilation of nitrogen from the air. Although this organism is polymorphic, cross 

 inoculation occurs. The leguminous nodules are discussed in four groups. 



