CHAPTER XXIX 



THE BEHAVIOUR OF PLANTS IN MASSES 

 (Report XVII) 



SINCE the toxin resulting from the growth of a plant acts on 

 other plants of the same nature, it must infallibly act also on the 

 plant producing it, and it will be impossible to grow any plant, 

 even by itself, without its being affected by toxin action. This 

 must be so in the pot experiments described in the preceding 

 chapters, even when the trays contain no surface crop, and the 

 only reason why the plants suffer so much more when there is a 

 surface crop in the trays, is that they then receive the toxin 

 from this crop, as well as that produced by their own growth : 

 on an average, the amount of toxin then affecting them will be 

 increased two- or three-fold. 



When a number of plants are grown side by side, some of the 

 toxin produced by each will become diffused through the soil, 

 and act on the neighbouring plants. When the space between 

 the plants is considerable, a certain portion of this toxin will 

 become oxidised before it reaches a neighbouring plant, and 

 hence spacing will diminish the general effect : but no arguments 

 as to the existence of toxic action can be based on such a result, 

 for increased spacing will at the same time increase the nourish- 

 ment of the plants, by allotting to each a larger bulk of soil 

 from which to draw its supplies. 



The toxic effect of one plant on another and on itself intro- 

 duces many novel factors which must be taken into consideration 

 when inquiring into the behaviour of massed plants ; and, for 

 investigations on the subject, pots were constructed so that a 

 number of plants could be grown together, with and without 

 root-interference. These were rectangular (Fig. 39, p. 292), 

 and all contained the same bulk of soil about 17 Ibs. but in 

 some cases they were divided into six separate compartments, 

 measuring 3 by 3 inches, and in the others they were not so 

 divided. 



