CH. Vl] TEMPERATURE. 145 



of the seeds : in jar B place a similar amount of 1 p.c. 

 NaCl solution. Measure again after 12 or 18 hours, when 

 the retarding effect of the salt solution should be obvious. 

 The roots in B only grow about half as much as those 

 in A. 



(170) Growth at various temperatures. 



A good rough notion of the effect of temperature may 

 be obtained by using the seeds of beans or peas. If a 

 considerable number of seeds are germinated, it is easy 

 to find 40 peas whose radicles, just emerging from the 

 micropyle, are of fairly uniform length. The}' are to 

 be sown, in 4 lots of 10 each, in small flower-pots. The 

 pots being covered with glass plates or saucers, are placed 

 (under otherwise uniform conditions) at temperatures of 

 39°_40= C, 35° C, 23° C, and at some fairly low tem- 

 perature, such as 10° — 12° C. The first three temperatures 

 can easily be kept fairly constant by means of thermostats, 

 the lower temperature may present difficulties at certain 

 times of the year. We employ a hollow- walled box, through 

 which a rapid current of tap water is allowed to run. 



After 48 hours measure again : the average growth of 

 the radicles at 10°— 12° C, 23° C, 35° C, will probably be 

 in ascending series, while the growth at 39° — 40° C. will be 

 less than that at 35° C. In one of our experiments the 

 average length of the radicles was after 48 hours : — 



Atl0°C. 5 mm. 



21 10 „ 



31 25 „ 



39-5 15 



D. A. 



10 



