Ill DEVELOPMENT AND ENVIRONMENT 77 



values shown are significant to plus or minus three per 

 cent. 



Firstly, we seem to have found a way of ascertaining 

 the depth of the root-system. The depth of the roots 

 had been measured by excavation at the end of May, and 

 the mean depth for the end of June calculated from this was 

 approximately 140 cm. ; this depth was the last at which 

 a loss of water was shown. A month later, at the end of 

 July, when the roots had grown another 50 cm. at least, 

 the samples from 160 cm. and 180 cm. also showed a 

 definite loss of water. This is not recommended as a 

 trustworthy way of finding mean root-depths, but it at 

 least adds an extra method to the scanty stock available 

 for root- investigation. 



For further interpretation of these data we obviously 

 need to intercalate observations at intermediate dates. 

 Certain points may however be deduced from them as 

 they stand. Thus, root-growth is not inhibited by soil- 

 water amounting to 80-90 per cent, of saturation. Again, 

 it would seem that less than 50 per cent, of saturation in 

 the soil is sufficient to produce water-shortage; on the 

 other hand, the pot experiments on this subject have 

 indicated that a lower value, perhaps 20 per cent., does 

 not usually limit growth at night ; the difierence must be 

 due to the fact that a large plant with a " limited " root- 



