CH. VI] TEMPERATURE. 133 



(170) Orowth at various temperatures. 



A good rough notion of Jihe 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°O., 35° C, 23° C, and at some fairly low tem- 

 perature, such as 10°-12° C. The first 3 temperatures 

 can easily be kept fairly constant by means of thermostats, 

 the lower temperature may present difficulties at certain 

 times of year. 



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 



Section B. Distribution. 



(171) Distribution of growth in roots^. 



Pick out a germinating bean with a root about 2 cm. 

 long. Make 5 marks, 2 mm. apart on the root, the 

 first mark being 2 mm. from the tip of the root-cap. 

 To mark the root, the seed should be pinned to a cork 

 plate and the millimeter scale raised on a layer of cork 

 pinned to the first named cork plate like a step, so that 



1 See Sachs' Arbeiten, l p. 414. 



