154 Some Factor h in Plant Competition 



showed clearly how powerful a factor a limited food supply is, but no 

 evidence was obtained as to the action of the light factor. To elucidate 

 this point water cultures were set up in which no shortage of food or 

 water was allowed to occur, but in which the light supply was varied by 

 the conditions of spacing. Sixty-four barley plants were placed separately 

 in nutrient solution and the bottles were packed in a square with eight 

 plants per side, as closely as possible, the distance from plant to plant 

 being 3| inches. Another 64 bottles, each wdth its plant, were arranged 

 on the greenhouse benches in the immediate vicinity of the crowded set, 

 but in this case each bottle was at least one foot away from its nearest 

 neighbour. Each bottle was kept in the same place throughout the 

 experiment, the nutrient solution being constantly changed to prevent 

 any lack of food or water introducing another factor of competition. 

 In this way it was hoped to obtain conditions of dense overcrowding on 

 the one hand, and absolute freedom from light competition on the 

 other, and the result justified the means. 



For the first five or six weeks, while the barley plants were quite 

 small and no overlapping of leaves occurred no difference was observed 

 in the growth of the spaced and crowded plants. As tillering began, the 

 crowded plants gradually seemed to improve more rapidly than the 

 spaced ones, though for some time it was doubtful if this were not merely 

 an optical illusion. After eight weeks' growth it was obvious that the 

 crowded plants were really the better. The leaves were decidedly larger 

 and broader, of a much darker green, while the spaced plants were 

 narrower in leaf and of a lighter yellowish colour, some plants sho\\'ing 

 a tendency to chlorotic stripes. At this stage a wet and dry bulb ther- 

 mometer was inserted amongst the leaves of the crowded plants, and 

 another was placed in the greenhouse away from the foliage. The 

 difference rapidly became still more marked, and a week later photo- 

 graphs were taken (Plate V, figs. 1 and 2). 



For the sake of a fair comparison the spaced plants were temporarily 

 crowded together (Plate V, fig. 2) in order to avoid giving the crowded 

 plants an unfair advantage due to optical illusion. 



A little later the succulence of the crowded plants was very noticeable, 

 the texture recalling that of marsh plants. The stems were very fleshy 

 and the plants, especially in the middle of the square, had begun to 

 depend upon their neighbours for support. The spaced plants at this 

 time appeared to be rather more tillered, and the tillers took full advan- 

 tage of the available space and spread out in rosettes on the tops of 

 the bottles. The leaves and shoots were much tougher and less easily 



