8 SEEOAGE. 



as they are oftener used in bud-propagation, ttiey are dis- 

 cussed in that connection. 



Bottom heat is helpful to germination in most seeds, but, 

 except in the case of certain tropical species, it should not 

 be strong. It is a common practice to place seed-boxes on 

 moderately cool pipes under benches in a greenhouse. Seeds 

 of hardy annuals and perennials do not require botton heat, 

 although they may be benefited by it. If the soil in seed- 

 beds should become too cool, watering with warm or tepid 

 water will be found to be helpful. 



It is impossible to give rules for the determination of the 

 proper temperature for different kinds of seeds. In general, 

 it may be said that seeds germinate most rapidly at a tem- 

 perature a few degrees above that required for the best 

 development of the plant itself. Seeds of hardy plants re- 

 quire a temperature of from 50° to 70°, conservatory plants 

 from 60° to 80°, and tropical or stove plants from 75° to 95°. 

 The plantlets should be removed from these highest tem- 

 peratures, as a rule, as soon as germination is completed. 



In outdoor culture, depth of planting has a direct relation 

 to temperature. Seeds may be planted deeper late in the 

 season than early, when the soil is cold and damp. Deep 

 planting probably as often kills seeds because of the absence 

 of sufficient heat as from the lack of oxygen or the great 

 depth of earth, through which the plantlet is unable to push. 



Influence of Light upon Germination. — The influence which 

 light exerts upon germination is not definitely understood 

 for all horticultural seeds. It is known, however, that seeds 

 will often germinate in full sunlight, if the proper conditions 

 of moisture and temperature can be maintained. Seeds 

 sown upon a moist surface and covered with a glass present 

 an interesting study. But it is well known, on the other 

 hand, that some seeds will not germinate, or will at least 

 appear unevenly, if subjected to sunlight. At least some of 

 the delphiniums, papavers and adonises germinate very 

 imperfectly, if at all, in direct light. It is always advisable 



