240 Relations between Growth and Envlronnicnt 



is well develojjed, but this check in root increase does not necessarily 

 imply a corresponding check to the shoot. 



Cessation of root increase is a constant phenomenon and always 

 occurs some time before the shoot stops growing. In some cases there 

 is evidence that an actual decrease in weight occurs after this period 

 but as this is most marked in the plants which are grown in constantly 

 changed food solution it is possible that the loss may be partly due to 

 abrasion in the mechanical process of handling, the loss not being made 

 good by growth. Without further information it is impossible to say 

 whether this loss of weight in the roots is of real significance, 



(2) Shoot growth and pod formation. 



As the duration of the tests was limited to a certain number of weeks 

 few of the series reached the stage of pod formation. Of these, three 

 received abundant food and one was limited in this respect. As soon as 

 pod formation begins the rate of growth of the stem and leaves, excluding 

 the reproductive organs, falls off immediately and relatively little extra 

 weight is put on, though the increase in weight of the whole shoot is 

 exceedingly rapid (Figs. 4 and 10). Up to the time of flowering the 

 energy of the plant is directed to building up a healthy body capable of 

 bearing the strain of reproduction. When seed formation begins the 

 energy is diverted into this channel, and the shoot (stem and leaves) 

 becomes merely the agent whereby the necessary materials for building 

 up the fruit and seed are supplied. Consequently it is now unnecessary 

 for more food to be expended in the production of a bigger shoot, so 

 little increase takes place and there is evidence that at a later stage still 

 loss of weight occurs owing to the transference of the actual substance 

 of the stem and leaves to the seed. This transference has been proved 

 in the case of certain other plants, among which barley and wheat may 

 be instanced^. The most rapid increase in the weight of the pods occurs 

 during the first two or three weeks after they appear, after which the 

 increase slackens oft" till eventually a drop in weight may occur associated 

 with the onset of maturation and desiccation. 



(3) Relation of nitrogen absorption to dry matter produced. 



A true estimate of the amount of nitrogen taken up can only be ob- 

 tained by analysis of the plant itself, but labour difficulties during the 

 wai- rendered it impossibh' lo have tbo necessary analyses mado. In 



' (a) Breiichley, W. K. and Hall, A. l).(ll>(»it). •• Dovolopmoiit df tlic CiJiiii of Wheat."' 

 Juarn. Aijric. Sci. Ul, pp. l!).o-2I7. 



(/>) Brcnchley, W. E.(l!)12). " Dcvclopiiu'iit ot the (iraiii oi Karlry." Ann. Bot.ww, 

 Ijp. 91:5-9:^8. 



