GERMINATION 105 



observations at intervals of twenty-four hours. When 

 most of the seeds in jar 5 (Sec. 139) have begun to sprout, 

 insert a thermometer and let it remain two or three min- 

 utes. Does it indicate any change of temperature ? Re- 

 fer to Section 29 and account for the change. If cotton 

 seed are used, the rise of temperature will be very marked. 



142. Vitality. — A very interesting point is to test the 

 temperature at which different seed lose their vitality, by 

 subjecting dry and soaked ones of various kinds to dif- 

 ferent degrees of heat and cold. Notice how the extremes 

 tolerated are affected by : first, the length of time the seeds 

 are exposed ; second, by the amount of water contained in 

 them ; and third, by the nature of the seed coats. Every 

 farmer knows that the effect of freezing is much more 

 injurious to plants or parts of plants when full of sap 

 (water) than when dry. This is because in freezing the 

 water expands and ruptures the tissues, thus setting up 

 internal disturbances which are liable to result in death, 

 especially if thawing takes place so rapidly that the life 

 processes have not time to readjust themselves. In like 

 manner it will be found that when seeds are subjected to 

 moist heat, they are killed at a lower temperature and in 

 a shorter time than when dry. When heated in water 

 of the same temperature, those seeds will be found to 

 resist best whose coats are most impervious to the 

 liquid. 



143. Time Required for Germination. — Arrange in a bed 

 of moist sand, placed between two soup plates, seeds of 

 various kinds. Good specimens would be some of the fol- 

 lowing : corn, wheat, peas, cotton, okra, turnip, apple, 

 morning-glory, orange, grape, persimmon, castor bean, pea- 

 nut, etc. Clip some of the harder ones and place them in 

 the same germinator with undipped ones. Keep all under 

 similar conditions as to temperature, moisture, etc., and 

 record the time required for each to sprout. What is the 

 effect of clipping, and why ? 



