REVIEWS 641 



3. Rate of stem growth was greatest during the first two weeks 

 after sowing, while the rates of growth in leaf surface and dry weight 

 were greatest in the last two weeks of the growth period of four weeks. 



4. Growth rates showed unmistakable seasonal marches increasing 

 in the first part of the season and decreasing in the autumn. These 

 marches were most apparent during the first two weeks of growth 

 from seed and were most clearly indicated by increase in stem height. 

 They corresponded in general to seasonal march of temperature 

 conditions. 



5. Range of seasonal march for both growth and temperature was 

 greater at Easton than at Oakland, with highest values at Easton. 

 Killing frost occurred earlier at Oakland, but the last period of two 

 weeks before frost at Oakland showed higher temperature and growth 

 values than for the same period at Easton, emphasizing the main 

 differences between a mild equable coast climate and a more rigorous 

 mountain climate, as they may influence plant growth. In the mild 

 coast climate with its low daily range, the frostless season is pro- 

 longed until growth is much reduced, or entirely checked by low 

 temperature. In the mountain climate at Oakland, however, with its 

 high daily range and high nocturnal radiation, very low night tempera- 

 tures and frost occur earlier in the season, while the day temperatures 

 and growth rates of many plants are still high. The maximum of 

 temperature and growth rates occurred a month earlier at Oakland 

 than at Easton. 



6. No relation was found between growth rates and either rainfall 

 or evaporation, probably because of auto-irrigation. The ratio of rain- 

 fall to evaporation had a secondary relation, however, in that greatest 

 leaf development during second fortnight occurred when this ratio was 

 highest. 



7. Temperature was clearly the limiting condition for growth 

 during the first two weeks after sowing, but for the last two weeks, 



r> 



the moisture ratio -^(-(rainfall divided by evaporation) appears to 



have been in many cases the limiting factor, especially with high tem- 

 peratures. It thus appears that if two plants in different stages of 

 development are exposed to the same fluctuations in environmental 

 conditions, the limiting condition for one plant during a succeeding 

 period may be of an entirely different nature from that for the other. 

 This is probably due to a difference between the internal conditions of 

 the plants at different developmental stages. 



