ON FREaH-WATER PLANTS. 243 



and require a very different process. But fresh-water Fresh-water 

 plants are still capable of comparison with others, since, on P'^"'^- 

 dissecting them, you directly perceive the same sort of 

 matter, as rind, bark, wood,^&c. The line of life forms the 

 centre, or meanders in it, and the air vessels are-generally 

 ranged next to it. I shall give the stem of the water lily as stem of the 

 the first specimen (see fig. 1, PI. VIT). I have said, that^^*"^'^* 

 the line of life is in the centre, where it forms a very thick 

 circle. The whole is then divided into six parts by the 

 bastard vessels, which pass from the centre to the circumfer- 

 ence. Six large cylinders fill up a part adjoining the line. 

 These are the air vessels, (see a a) ; and the rest of the 

 space is occupied by the pith, sprinkled with wood vessels. 

 The circumference is bounded with a few rows.of bark, en* 

 closing some inner bark vessels, and a rind surrounds the 

 whole. This, with the figure, will give a general idea of it. 



But it is necessary to give some description of the air vessel, its air vessels. 

 which is really curious in its formation. It is a large cylin- 

 der, divided at every half inch of its length ivith a thin 

 texture of pith : but lest this should not be sufficient to 

 prevent insects from entering it, and choking up the vessel, 

 as soon as the plant sinks in the water, a quantity of hairs. Hairs, 

 which are placed in circles in the interior, rise, and, meeting 

 in the centre, not only aid to keep out the water, but 

 run through every insect, that ventures to approach. I have 

 often caught insects threaded on the hairs, but they ere 

 soon washed off. Sometimes the hairs remain in a horizon- 

 tal position; but in general they rise and fall with the water. 

 This, exciting my curiosity, made me anxious to apply to 

 the solar microscope for the discovery of the mechanism, 

 which regulated the motion of the hairs: and I found, that, 

 though there was no spiral wire in the other parts of the 

 plant, it was to be found in the hairs. The formation was 

 simple, and merely caused by the contracting and dilating 

 of the wire, as the hairs were drawn up, and ranged against 

 the side of the cylinder, or placed themselves horizontally, 

 their points meetiug in the centre. The wood vessels are Wocd vessdi^ 

 to be distinguished from the buds by their inferior size and 

 and circular ^ape. The buds (as in most annual plants) Budsi 

 proceed from the root ; and of course have a stem shooting 

 R 3 thende, 



