Temperature 343 



vegetative phase, however, did not result in the production of more plant 



material. 



L. D. Tukey ( 1952 ) subjected bearing branches of sour cherry to sev- 

 eral different night temperatures and found that higher temperatures 

 accelerated development during stages I and II (early growth and stone 

 formation) but checked it in stage III (fleshy pericarp growth) (Fig. 



2-5). . . 



Leopold and Guernsey (1954) treated germinating peas with various 



growth substances and followed this with low temperature. The combi- 

 nation of chemical with temperature stimulation they termed chemical 

 vernalization. It hastened flowering, but only if carbon dioxide was later 

 present. Changes in day-length had no effect. They conclude that there 

 are two stages in the growth of young pea plants which are affected, the 

 first requiring auxin and low temperature and the second requiring 

 carbon dioxide. The function of carbon dioxide here is not understood. 



Chaudri, Biinning, and Haupt (1956) observed that the exposure of 

 young onion plants to 3 hours of low temperature during the dark por- 

 tion of the photoperiod hastened the development of bulbs. This effect 

 was greatest when the low temperature was applied during the latter 

 part of the dark period. 



Fisher ( 1954 ) worked with a trifoliate New Zealand species of Ranun- 

 culus in which the juvenile leaves are undivided. Sometimes the adult ones 

 show a partial reversion to this juvenile form. He grew plants under 

 controlled conditions and found that when the temperature was relatively 

 high (20°C in the daytime and 15°C at night) there was a complete 

 reversion to the undivided juvenile leaf shape but that at lower tem- 

 peratures ( 10 and 5° ) the adult form persisted. 



Steinberg (1953) studied Mammoth Rustica tobacco, a type which 

 came originally from a cross between Nicotiana rustica and N. tabacum. 

 This is indeterminate in growth and very rarely flowers, but it can 

 readily be made to do so if the night temperatures are dropped to 50 

 or 60°F, regardless of day-length. In this respect it is unlike Maryland 

 Mammoth (p. 316), which also is indeterminate in growth but flowers only 

 in short days, regardless of temperature. The indeterminate character of 

 growth in both is due to the fact that flowering is prevented, in one type 

 by high temperature and in the other by long days. Steinberg suggests 

 that there may be a separate genetic basis for the two types of reaction. 



Benson-Evans and Hughes ( 1955 ) observed that in the liverwort 

 Lunularia cruciata, which is world-wide in distribution but rarely repro- 

 duces sexually except in a "Mediterranean" type of climate, the induc- 

 tion of archegoniophores requires subjection to low temperature, later 

 followed by higher temperature and long days, thus fitting it to its par- 

 ticular ecological distribution. 



