20 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS 



each. Put in each vessel the same number of soaked peas of about 

 the same size. Stand the vessels with their contents in places 

 where they will be exposed to different, but fairly "constant, tem- 

 peratures, and the same conditions as regards light, and observe 

 the several temperatures carefully with a thermometer. Take 

 pains to keep the tumblers in the warm places from drying out, 

 so that their contents will not be less moist than those of the 

 others. The following series is merely suggested; other values 

 may be found more convenient. Note the rate of germination in 

 each place and record in tabular form as follows : 



No. of seeds sprouted in 24 hr. 48 hr. 72 hr. 96 hr. etc. 



At 32° F. (0° C.) 



At 50° F. (10° C.) 



At 70° F. (21° C.) 



At 90° F. (32° C.) 



If a thermostat can be had, it should be used to control the 

 temperatures, and the highest point at which germination can 

 take place should be noted. 



EXPERIMENT II 



Amount of water in air-diy seeds and amount absorbed to produce germination. 



A. Weigh accurately a convenient quantity of seeds, and then dry them 

 on the water bath until they no longer lose weight.^ Report the loss of 

 weight as water and calculate what per cent it constituted of the total 

 weight. 



B. Weigh a new set of seeds from the original (undried) lot, place them 

 between layers of porous white paper kept thoroughly moist but not 

 dripping wet, cover them, and allow them to remain until the germina- 

 tion is evidently begun. Reweigh the seeds, and calculate the increase 

 of weight by absorption of wa.ter and the per cent of absorbed water.2 



This last will be 



weight water absorbed 



weight air-dry seeds 



1 This may be done once for ajl for the entire laboratory division. 



2 The gain in weight observed may be a trifle less than the total value, since 

 some loss of weight by oxidation is certain to have occurred. 



