482 Principles of Gardening 



should not exceed more than from ten to twenty tunes their 

 bulk, and all communication with the surrounding atmosphere 

 be cut off, so that the water may not absorb any oxygen from it, 

 the seeds do not germinate, although placed in a sufficiently 

 hio-h temperature ; when the same experiment is repeated with 

 a proportionately larger quantity of water, they find in it suffi- 

 cient oxygen to enable them to germinate. Old seeds germinate 

 sooner in pure oxygen than in atmospheric air, when oxygen is 

 by degrees absorbed, and carbonic acid given out. As is well 

 known, the absorbed oxygen burns (verbrennt) with the carbon 

 of the plant, and thereby forms the carbonic acid, which is 

 emitted; this may be considered as a sort of breathing process, 

 by which, when, as in this case, it takes place in a high degree, 

 it produces the high temperature which is observable in ger- 

 minating seeds when many are together. Thus, nature wisely 

 provides that the necessary heat for the process of assimilation 

 of the reserved nourishment should be increased by this pro- 

 perty of the seed in germinating. 



Under 3° of Reaumur (40° Fahrenheit), the seeds of our 

 native plants do not germinate ; while those of the tropics, the 

 functions of which proceed more rapidly, require a pro- 

 portionately higher temperature. Dry seeds stand so high a 

 degree of cold, that even the lowest temperature of the frigid 

 zone does not injure them. But, if they have imbibed any 

 moisture, they freeze in proportion to the state of growth that 

 had been excited, and according to the climate of their native 

 zone; for cold, as will be shown in another chapter, only kills by 

 the sudden interruption of vegetation or life. Too high a de- 

 gree of heat is, on the contrary, injurious to seeds ; and, when 

 continued for several days, they are killed at a temperature of 

 from S5° to 40° Reaumur (111° to 122° Fahrenheit), while, for 

 a short time, they could stand 60° of Reaumur (167° Fahren- 

 heit), if quite dry. For this reason, we should avoid exposing 

 the seed in seed-rooms to the direct heat of the stove, or drying 

 them on the stove, as they then invariably lose their power of 

 germination. 



Plants of the temperate zones, when there is a sufficient 

 quantity of them, are generally sown, in the Botanic Garden, in 

 the open ground, or in shallow pans, which are placed in open 

 pits, where they can be protected from heavy rain, which would 

 wash them up ; for the admission of the free air, on account of 

 the great quantity of oxygen it contains, is very favourable 

 to germination. The seeds of the warmer zones, as well as of 

 those annuals which, on account of our short summer, must be 

 sown early in order to ripen their seeds, are put in beds lined 

 with a mixture of half horse-dung and half leaves ; because 

 these materials do not become heated to such a deiiree as 



