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. 



(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. They 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 tempera- 

 tures can easily be kept fairly constant by means of ther- 

 mostats, 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 : 



AtlOC. 5mm. 



21 10 



31 25 



39-5 15 



D. A. 10 



