198 Effect of Temperature and Insolation upon Groioth 



From a comparatively early date the advantage seemed to be with 

 the spaced plants, and became more marked as growth proceeded and 

 the intensity of light decreased with the waning season. The difference 

 in shoot growth was not noticeable for several weeks, but the roots of 

 the spaced plants soon became strong and bunchy, being larger than any 

 of the crowded roots. In the latter the roots on the outside were com- 

 paratively strong, but decreased steadily in size towards the middle of 

 the square, where they were fairly long but very thin. At harvest-time 

 the spaced plants were strong and healthy, well branched, bearing plenty 

 of long well-filled pods, while the roots were very strong. In the crowded 

 square, on the other hand, the middle plants were obviously smaller in 

 all respects than the outer, the difference being now as noticeable in the 

 shoots as in the roots. Most of the pods were thin and distorted, and the 

 seeds had not developed properly. 



Table I. 

 Dry Weights. [Mean figures.) 



The above table shows how seriously the reduction of light due to 

 overcrowding affected the growth of peas. A large reduction in dry weight 

 and efficiency index occurred at the outer edge of the square, although 

 one side of each plant was free from light competition, and this reduction 

 was intensified inside the square, where shading came on all sides. Apart 

 from the outer row the differences between the plants were not very 

 marked, showing how effective is the shading of pea plants by their 

 neighbours when in close proximity. Broadly speaking, these results 

 are comparable with those obtained for barley, and indicate a similar 

 reaction of broad- and narrow-leaved plants to fight deficiency. The per- 

 centage of nitrogen in the spaced plants was lower than in the crowded 

 ones, being only 3-62 per cent, against 4-15 per cent. As with barley this 

 probably shows that peas utilise less nitrogen in the production of each 

 unit of dry matter when adequate illumination is available. 



When, however, the above experiment was carried on under con- 

 ditions of very high temperature and prolonged intense sunshine, certain 



