Durability of the Ferns. 281 



them ; and that they fall down again, as soon as the heat of 

 the sun begins to be perceived. In comparing the increase in 

 weight when exposed to dew, in plants thickly furnished with 

 hairs, and possessing few or no stomata, with that manifested 

 by plants having a smooth surface and no stomata, it is seen 

 that the former is much the greatest ; and that it also surpasses 

 in about the same proportion the weight gained by immersing 

 the footstalk in water. Thus two heads of common Hore- 

 hound, the original weight of which was fifteen grains each, 

 W ere placed, one with its stalk in water, and the other in a 

 place exposed to dew, for a night ; the first was found to have 

 gained two grains, and the second five grains. Both were ex- 

 posed to dew during the next night, and on the following 

 morning they each weighed twenty-three grains, each having 

 gained eight grains, of which the first had acquired six in that 

 night. A withered stem of Alpine Chickweed, weighing five 

 grains, gained six grains by exposure to dew for two nights. 



DURABILITY OF THE FERNS. 



The great preponderance of the ferns, and of the higher or- 

 ders of the Cryptogamic plants, in the Flora of the ancient 

 world, having excited, in a peculiar degree, the attention of 

 naturalists, and it being conceived that the total absence of cer- 

 tain kinds of plants, and the constant presence of others, with 

 other points of the like nature and interest, might be accounted 

 for by a difference in the capability of one plant to resist the 

 action of water beyond another, Dr. Lindley resolved to try 

 the result by actual experiment. 



He therefore, on the 21st of March, 1833, filled a large iron 

 tank with water, and immersed in it 177 specimens of various 

 plants belonging to the more remarkable natural orders, taking 

 care, in particular, to include representatives of all those 

 which are constantly present in the fossil state, or as univer- 

 sally absent. The vessel was placed in the open air, left un- 

 covered, and was untouched, with the exception of filling up 



