4oz 



THE QUARTERLY REVIEW OF BIOLOGY 



periments is secured. Each seed is in- 

 dividually weighed and measured and the 

 selection of the seeds to be used based 

 upon these quantitative data. Then, 

 under aseptic precautions, the testa is 

 removed from each selected seed. The 

 shelled seeds are then sterilized by im- 

 mersion for one minute, with stirring, in a 

 1:1000 bichloride of mercury solution, 

 following by rinsing in sterile, distilled 

 water. The seeds are then soaked for 

 three hours in sterile distilled water, in 

 such a way as to ensure that each seed is 

 not in contact with any other, and that 



ing. A richly branched root system de- 

 velops in the agar substrate. Above it 

 rises a straight unbranched stem, bearing 

 the cotyledons at its top. 



The period of growth is followed by the 

 ■period of suspended animation. After growth 

 has ended the seedling remains without 

 visible change for a varying number of 

 days, not growing but still living, with 

 cells in full turgor, and in every way 

 entirely normal in appearance. The plant 

 is living and carrying on metabolism, but 

 it has stopped growing. 



The period of suspended animation is 



Period 



of 

 Growth 



Period of Suspended 

 Animation 



Total duration of life 



Beginning 



deaih 



Fig. 8. Diagram to Show the Course of Events in an Experiment on Inherent Vitality with Cantbloup 



Seeds as Material 



therefore all have an equal chance to 

 absorb water. After soaking, one seed is 

 carefully placed on the top of the agar in 

 each tube. The tube is then tightly sealed 

 with a sterile cork or with sterile cotton. 

 The tubes are placed in light-tight boxes 

 and put in an electric incubator running 

 at 30°C. 



What happens in such an experiment is 

 shown schematically in figure 8. In this 

 diagram the horizontal scale represents 

 time and the vertical scale the size of the 

 seedling plant. 



There is first the period of growth . During 

 this period the seedling is actively grow- 



followed by the period of death. A time 

 comes when the seedling begins to die. 

 Death is a progressive process which re- 

 quires a number of days to complete. The 

 gradual progressive nature of the death of 

 the seedling makes a practical trouble in 

 the experiments. It is difficult to decide 

 upon and to read an end-point of total 

 duration of life. The series of events 

 involved in the death of the plant are 

 nowhere sharply and precisely delimited. 

 The stages grade into each other by a 

 gradual continuous process difficult to 

 break up observationally into discon- 

 tinuous phases, for the simple reason that 



