Page:An introduction to physiological and systematical botany (1st edition).djvu/124

 94 former the young plants rose to the height of two inches, or more, in a week's time; in the other none appeared, till after the pot had been removed for a similar period into the air again. Seeds buried in the ground to a greater depth than is natural to them do not vegetate, but they often retain their power of vegetation for an unlimited period. Earth taken from a considerable depth will, when exposed to the air, be soon covered with young plants, especially of Thistles, or of the Cress or Mustard kind, though no seeds have been allowed to have access to it. If the ground in old-established botanic gardens be dug much deeper than ordinary, it frequently happens that species which have been long lost are recovered, from their seeds being latent in the soil, as I have been assured by Mr. Fairbairn of Chelsea garden, and others.

The integuments of the seed, having fulfilled their destined office of protection, burst and decay. The young root is the first part of the infant plant that comes forth, and by an unerring law of Nature it is sent downwards, to seek out nourishment as well as to fix the plant to the ground. In sea-weeds,