66 BIOLOGY AND HUMAN LIFE 



the one or many substances which might perhaps cause sprout- 

 ing cannot get into the seeds in the dry state. We should there- 

 fore try these substances with water. That, however, at once 

 raises the question, Has water by itself any effect on the sprout- 

 ing seeds? We should therefore proceed to experiment with 



pure water. 



55. Relation of water to sprouting. We may place a number 

 of seeds in each of several vessels with various quantities of 

 water, while other seeds from the same lot are kept under 

 similar conditions of air, light, and temperature but without 

 water. The results should convince us that one of the conditions 

 necessary for starting the germination of the seeds is the pres- 

 ence of a certain amount of water. 



We shall find also that some kinds of seeds will fail to sprout if they 

 are completely covered with water, although other kinds will sprout 

 under water. The seeds in the first class are not injured by water; the 

 liquid simply prevents them from absorbing sufficient quantities of air. 



56. Relation of temperature. It may be that other factors also 

 play a part. For example, seeds in the presence of water may 

 sprout at one temperature but not at another. From actual 

 experience with seeds of different species of plants we know 

 that some kinds may be safely sown earlier in the spring than 

 others. From experiments we can also learn that some seeds 

 will fail to sprout when it is too cold or too warm. A systematic 

 experiment in which several groups of seeds with water are 

 placed so that each set is in a different temperature will satisfy 

 us ( I ) that there is a point at which the sprouting proceeds most 

 quickly, and (2) that there is a limit in the range of temperature 

 for the sprouting of every species of seed. 



57. Relation of air. Is the presence of water at a favorable 

 temperature not enough by itself to cause the seeds to sprout? 

 The air may perhaps influence the activity of the young plant 

 after water is absorbed. Experiments can show us whether air 

 is necessary for sprouting in addition to water. In the same 

 way we can go on and try out the possible influence of light. 



