THE CONDITIONS OF LIFE 27 



conditions may suggest that the one or many substances that 

 perhaps can cause sprouting would fail under the conditions of 

 the experiment because the dry substances cannot get into the 

 seeds. We should therefore try these substances in connection 

 with water. That, however, at once raises the question whether 

 water by itself has any effect on the sprouting of seeds. 



42. Relation of water to sprouting. We should therefore 

 proceed to experiment with pure water. An experiment in which 

 some seeds are placed with various amounts of water, while 

 other seeds from the same lot are kept under similar conditions 

 of air, light, and temperature, but without water, will easily 

 convince us that one of the conditions necessary for starting 

 the germination of the seeds is the presence 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. 



43. 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, and that some seeds will fail to sprout when it is too 

 cold or too warm. By means of a systematic experiment in 

 which groups of seeds with water are placed in a number of 

 different places having different temperatures, we may satisfy 

 ourselves that there is a limit in the range of temperature for 

 the sprouting of every species of seed, and that there is a 

 point at which the sprouting proceeds most quickly. 



44. Relation of air. It may also be that the presence of 

 water at a favorable temperature is not enough to cause the 

 seeds to sprout. The air may perhaps influence the activity 

 of the young plant after water is absorbed. Experiments may 



