PHYSIOLOGY. 283 
is, to consider it as an action of the vital power. 
Dr Percival’s assertion indeed appears to me to be 
a very precipitate conclusion. 
6 244, 
It deserves our attention too, that not all seeds have 
the rostel, especially of some aquatic and parasitic 
plants, and perhaps all those which Dr Gaertner 
styles acotyledones. was, as far as 1 know, the first 
who discovered this, when I examined with great 
eare the water-caltrops, (rapa natans), one of the 
most singular plants. ‘Uhe nuts, as they are called, 
of it, when they lie in water, the natural habita. 
tion of the plant, shoot forth a long plumule, which 
in a perpendicular direction rises towards the sur- 
face of the water, its sides push out at certain 
‘distances, capillary, branched leaves Some of those 
leaves bend downwards and attach themselves at the 
bottom. Here then the piant becomes fixed in the 
ground, not by a peculiar root, which, as rostel, pre- 
existed in the seed, but only through the leaves, 
It would be as difficult as in the rostel, to state the 
reason, why some of the undermost leaves bend 
downwards, and from their capillary extremities 
shoot forth roots. | 
From this, however, we are enabled to conclude, 
that some seeds may want the rostel; but that a ger- 
minating seed should perform its functions without 
plumule and cotyledons, is impossible. Nobody a: 
yet has attempted to deny the existence of the ae 
mule in any seed, Linné, Gaertner, Jussieu, and 
many 
