76 



SEEDS AND SEEDLINGS 



general way it may be said that an oversupply of water will pre- 

 vent growth of seeds almost as effectually as no water at all. In gen- 

 eral the amount most favorable for germination is a moderate supply. 

 We shall find that although plants may live for a consider- 

 able time in water or in sawdust or other materials weU moistened 

 in water, yet soil is an essential to the growth of most seed plants. 

 Some plants, as some orchids and " Spanish moss " (a true seed 

 plant), may exist without any connection with soil. Yet most 

 plants need soil water and take from the soil materials needed to 

 make up their living matter. 



Moderate Temperature Best. — Another factor influencing the 

 germination of seeds is that of temperature. The temperature at 

 which different seeds germinate varies greatly. Those of you 

 who have a garden at home know that even some varieties of seeds 

 germinate at lower temperatures than others of the same species; 

 for example, early peas, lettuce, or radish seed. As a general rule, 

 increase in temperature is favorable up to a certain point, beyond 

 which it is injurious to the young plant, and seeds exposed to a mod- 

 erate temperature do better in the long run than those in the heat. 

 Light has a certain marked effect on young seedlings, which 



will be considered when we take up 

 the growth of the stem in more 

 detail. 



Some Part of the Air a Factor. — 

 We have already considered the 

 chemical composition of the air in 

 its place as part of the environment 

 of plants and animals. But few of 

 us reason out why air is a necessary 

 factor in the growth of plants and 

 animals. 



It is an easy matter to prove that 

 peas or beans will not germinate 

 without a supply of air. Equal 

 numbers of soaked peas, placed in 

 two bottles, one tightly stoppered, the other having no stopper, 

 both bottles being exposed to identical conditions of light, tem- 

 perature, and moisture, show that the seeds in both bottles start 



Experiment to show the effect of lack 

 of air on germination. 



