•376 On Spontaneous Generation. 



a plant not otherwise met with in Denmark. In the same 

 country, Mr. Hofman of Hofmansgave made a very curious 

 observation in 1821 and 1822. An arm of the sea having been 

 laid dry, by the construction of a dyke, the whole of the 500 

 acres of ground thus obtained was covered, within two years, 

 with Arenaria marina, which even during the first year had 

 made its appearance on the most favourable spots. This phe- 

 nomenon, though interesting in our point of view, was less so 

 than the one offered by a single spot of that drained area, 

 where fresh water oozed through the ground. There, and 

 there only, grew Juncus bulbosus, Scirpus lacustris, Ttanun- 

 lus sceleratus, Cineraria palustris, Epilobium hirsutum, and 

 Chenopodium album; plants otherwise not found on sea- 

 ground laid dry. Professor Schouw, of Copenhagen,* tried 

 to explain all these phenomena by supposing that the seeds 

 of some of the plants, being furnished with & pappus, had been 

 brought to the spot by the wind, others by birds, others again 

 by the fresh water oozing through the ground. I make no 

 doubt that wind, birds, and water, act an important part in 

 conveying the seeds of plants to spots where the respective 

 species have not been observed before ; but these agents are 

 quite inadmissible in many cases. Leaving the seeds furnish- 

 ed with a pappus, and their vehicle, the air, out of the ques- 

 tion, there are many not enveloped in berries, &c. of which 

 every single grain is crushed by the birds which ijeed on them, 

 before they are swallowed, and yet we see their species grow- 

 ing at once on spots, whither they cannot have been carried 

 by water, because they do not grow on any more elevated 

 ground of the same hydrographical district, as soon as those 

 spots have undergone an appropriate change. To prove this, 

 I shall refer to an observation which I had an opportunity of 

 making many years ago, and which I believe may be verified 

 in many localities. A road was constructedf along the north- 

 ern slope of a limestone hill, containing Ammonites, &c. and 

 overlaid up to the middle with plastic clay. The road was 

 cut through this clay, and in one spot opened a small vein of 

 water, which before could not make its appearance above 

 ground, on account of the impermeable nature of the clay. — 

 The water formed a long pool in the narrow ditch on the up- 

 per side of the road, in which, the year after, grew in great 

 abundance, Veronica Beccabunga and Festuca fluitans. The 

 nearest localities for these two plants, are to the right and left 

 of that spot, at the distance of about half an English mile, 



* See Tidsskrift for Naturwidenskaberne, N. 1 & seq. 

 | Near tlie town of Waltershausen, in the duchy of Gotha. 



