294 GERMINATION KEQUISITES FOR IT. 



on Auricula seeds, some of which were covered by a transparent bell- 

 jar, others by a jar of ground glass, and a third set by a jar enveloped 

 in black cloth. The last germinated most rapidly. Mr. Hunt says 

 that the luminous or light-giving rays, and those nearest the yellow, 

 have a marked effect in impeding germination ; the red or heat-giving 

 rays are favourable to the process, if abundance of water is present ; 

 while the blue rays, or those concerned in chemical action or actinism, 

 accelerate the process and cause rapid growth. His experiments were 

 performed by making the sun's rays pass through different kinds of 

 coloured glass. He believes that the scorching effect of the sun on 

 leaves may be prevented by the use of blue glass, and that a high 

 temperature might be obtained by red glass. He has suggested a 

 pale-green glass made with oxide of copper, as that best fitted for con- 

 servatories. By this means he expects that the scorching rays of 

 light will be excluded, while no hinderance is given to the passage of 

 the others ; the green colour being a compound of yellow or luminous, 

 and of blue or chemical rays. A delicate emerald-green glass has 

 been employed lately at his suggestion, in glazing the large Palm- 

 house at Kew. 



614. Some have said that electricity prevents germination, but facts 

 are wanting to confirm this. The experiments of Dr. Fyfe,* Mechi, 

 Coventry, and others, have shown that the statements made in regard 

 to the efficacy of electro-culture are erroneous. 



615. In order that plants may germinate vigorously, moisture, heat, 

 and air must be supplied in due proportion. If any of them are de- 

 ficient, or in excess, injury may be done. It is of great importance, 

 therefore, in agricultural operations, that the ground should be well 

 pulverized, the seeds regularly sown at a proper and equal depth, and 

 the soil drained. Pulverized soil, when examined, is found to consist 

 of small particles having cavities in their interior, and separated from 

 each other by interstitial spaces. In a very dry soil, all these cavities 

 are full of air ; in a very wet undrained soil, they are full of moisture ; 

 while in a perfectly drained soil, the interstices are full of air, while 

 the particles themselves are moist. The seed in such a soil is under 

 the influence of heat, air, and moisture, and is excluded from light. 

 Hence it is in very favourable circumstances for germination. Frost 

 has an important effect in pulverizing the soil, by the expansion of the 

 water contained in the particles, when it is converted into ice. Snow, 

 again, acts in giving a covering to the young plant, protecting it from 

 intense frost and sudden alternations of temperature, and by its slow 

 "melting allows the plant to accommodate itself to the mild atmosphere. 

 Snow contains often much oxygen. 



616. If a field is not equally planted, the seeds will sink to different 

 depths, and will spring up very irregularly. The seeds should be 



* See Trans, of Soc. of Arts, voL iii. part ii. p. 109. 



