650 KANSAS CITY REVIEW OF SCIENCE. 



TOTAL WEIGHT. 



Seeds 8.626 



Plant 4.429 



Difference 4- 097 



thus showing a loss of more than one-half of the solid substance of tlie seed dur- 

 ing germination. . The process by which this matter disappears from the seed is 

 a real combustion and results in the elevation of the temperature of the seed to a 

 greater or less degree. 



The necessity of the presence of air to the germinating seed leads to the nec- 

 essary conclusion that if seeds are buried so deeply in soil, or so surrounded by 

 water as to exclude the air, germination cannot take place. The seeds may rot 

 but they cannot grow. 



This leads to a consideration of the question as to the depth at which seeds 

 should be planted. This will be found to depend upon a variety of circumstances. 

 It is evident that a small seed should not be planted as deeply as a large one. 

 The depth should also vary with the climate and the soil. In a dry climate or a 

 porous soil the seeds must be buried to a greater depth than if the reverse be true. 



This is necessary that the requisite amount of moisture may be secured at 

 the same time the aridity or porosity of the soil is more permeable to air, thus in- 

 suring a supply of oxygen to the germinating seed at a greater depth than if the 

 soil were compact or saturated. In some very dry countries it is necessary to 

 bury seeds at a much greater depth than would be safe under other conditions. 

 Thus it is said that the Indians on some of the dry plains of Colorado plant their 

 corn ten to twelve inches deep, by this means securing sufificient moisture to in- 

 sure its germination and growth, which it would not have if planted at a much 

 less depth. As a general rule, in ordinary agricultural soil seeds may be planted 

 to a depth of about five times their diameter with fair promise of success, varying 

 from this according to the condition of the soil as to compactness and moisture. 



The limits of certain degrees of temperature are also essential to the healthy 

 germination of seed. The seeds of some arctic and alpine plants are known to 

 germinate at the temperature of melting ice, while some of a tropical habitat re- 

 quire a temperature equal to that of our hottest days to awaken their germs into 

 active life. Between these extremes seeds are found germinating at every varia- 

 tion and degree of temperature. For all species of seeds there are certain limits 

 above or below which they will not germinate. These limits vary, of course, 

 with the different kinds of seeds. 



The following table, given by Johnson, (How Crops Grow, p. 133,) shows the 

 extreme temperatures between which some of our most common agricultural 

 plants germinate, and also the degree at which the process takes place most 

 rapidly: 



