396 MARGARET S. JARVIS 



difference wliich might have existed between the species with respect to this 

 particular response. 



Thus the resuks from these experiments supplement the conclusions 

 drawn from the results of the soil moisture regime experiments. The 

 northern species, 5. hypnoides and P. padus, were more sensitive to the effect 

 of increase in SMT in depressing their rate of growth than were the 

 southern species, F. vulgaris and T. sangiiiiiea. 



120- 



100- 



80 



V 



o 



Z 60 



U- 



< 



LJ 



< 40- 



9 



20 



6 10 12 14 16 18 20 22 

 TIME IN DAYS (FEB. I960) 



24 26 28 



Fig. 2. Saxifraga liypiioidcs. The effect of soil moisture tension on the rate of increase 

 of total leaf length. (1-29 February i960.) For details see text. Container numbers 

 are at the ends of the curves. Soil water tensions (atm) are shown beside each point. 

 The soil was watered thoroughly at points marked W. Plants in container 6 were not 

 subjected to drying-out after day 8. 



THE RELATION BETWEEN SOIL MOISTURE, LEAF 

 WATERDEFICIT AND TRANSPIRATION RATE 



Differences, in response to changing SMT, in the leaf growth of different 

 species may arise in several ways; firstly, through different degrees of 



