ON PROPAGATION BY SEED. 243 



seeds, with moss. The more tender kinds are also sown in frames, or under 

 hand or bell glasses, by which evaporation is prevented or checked, and a 

 steady degree of moisture effectually maintained. 



556. The water requisite to cause old seeds to germinate should be more gradu- 

 ally given to them, than that given to vigorous young seeds; because the power 

 of absorbing water in old seeds is not diminished in the same proportion as 

 their power of decomposing it. When old seeds are placed hi moist soil, they 

 are consequently very liable to rot ; more especially, if the temperature be 

 not somewhat higher than new seeds of the same species usually require. 

 Hence, old seeds should be sown in a much drier soil than new seeds, and 

 should be supplied with water much more sparingly, or left to absorb it from 

 the atmosphere. Very old seeds will, however, sometimes germinate 

 quickly by being steeped for some days in warm water ; and M. Regel men- 

 tions an instance of this, with regard to some very old seeds of Umbelliferae. 

 In the botanic garden at Bonn, in the spring of 1838, four pans were sown 

 with seeds, full ten years old, of Ferula tingitana, />., in which the embryo 

 seemed entirely dried up, and only those in two of the pans were previously 

 soaked. The latter sprang up all together in from ten to twenty days, while 

 of those in the other pans, which were left for trial, only a few plants came 

 up in one pan in the spring of the following year, the rest of the seed having 

 all rotted. (Gard. Mag. for 1841, p. 485.) 



557. The depth to which a need is buried in the soil has, for its chief object, 

 the maintenance of a due degree of moisture, but another purpose is to exclude 

 the light, and to give the future plant a better hold of the ground ; though 

 there is no seed whatever that will not vegetate on the surface, if that sur- 

 face be kept uniformly moist and shaded. It may be assumed that every 

 seed will vegetate and establish itself in the soil, if buried to its own thick- 

 ness ; but the experience of gardeners proves, that some large seeds, sucli as 

 leguminous seeds, nuts, &c., make better plants when buried much deeper. 



558. The degree of heat most favourable for the germination of seeds may 

 be considered as that best adapted for the growth of the parent plants ; and, 

 hence, if the native country of any plant is known, it may be assumed that 

 the seeds will germinate best in the temperature of the spring, or growing 

 season of that country. Some seeds of cold climates, such as those of the 

 common annual grass, duckweed, groundsel, &c., will germinate in a tem- 

 perature little above the freezing point; but, in general, few northern 

 plants will germinate under 40% and the most favourable temperature for 

 germinating Dr. Lindley states to be for the seeds of cold countries, from 

 50 to 55 ; for seeds of greenhouse plants, from 60 to 65 ; and for seeds 

 of the plants of the torrid zone, 70 to 80. (Theory of Hort., p. 166). It 

 may be remarked that though the seeds of warm countries will not vegetate 

 in the temperature of cold countries, yet that the reverse of this does not 

 hold true, as may be observed in the germination of British weeds in our 

 stoves ; but the plants thus produced, unless immediately removed to the 

 open air, remain weak and sickly. 



559. The degree of heat which the seeds of plants will endure has already 

 been slightly noticed. Certain leguminous seeds, as those of some acacias, 

 may be subjected to the boiling point for a few minutes without injury ; 

 others may be allowed to steep and cool for twenty-four hours in water 

 heated to 200. The seeds of Acacia Lophantha were subjected to boiling- 

 water for five minutes, and the plants raised from them were exhibited before 



