230 PHILOSOPHICAL TRANSACTIONS. [anNO I675. 



bark becomes to be an aggregate of reticular coats, surrounding the woody part 

 of the plant: and as to what passes through them, he says, that the juice being 

 entered into them, is, by the heat of the season striking upon the soil and forcing 

 up the liquor, made to ascend a little way ; and then by the survening night and 

 cold stopped for the time, but is again, by the heat of the next day sendirjg up 

 more juice, thrust up higher from time to time, till it gets to the top, climbing 

 thither as it were by steps: to which ascent it is marvellously assisted by the 

 structure of these pipes, being divided into square partitions, opening into one 

 another, and furnished with something that performs the part of valves, endued 

 with a spring. 



From these pipes, he says, do depend and break forth horizontal ranks of bags 

 or bubbles, crossing those fibres ; into which bubbles the ascending juice, like a 

 chyle, is discharged, and being stayed there a while, and mixed with the old juice 

 there residing, comes to be fermented and convei'ted into aliment. 



But besides this preparation of the aliment in the bark, there is another office, 

 which that part seems to be appointed for; and that is the increase of the bulk 

 of plants, by adding yearly a coat or ring of fibres, which being interwoven by 

 the above-mentioned horizontal ranks of bubbles, and by degrees consolidated 

 and hardened, do put on the nature of wood. 



The stem or trunk of plants consists, according to him, of ligneous fibres, 

 transverse ranks of bubbles, and air-pipes. In young trees, he says, the ranks 

 of these bubbles pass into the very pith ; which pith is abounding in young 

 twigs, until by the growth and hardening of the ligneous fibres it wastes away. 



The air-pipes, called also by him spiral fibres, are in his opinion, a kind of 

 silver-coloured plate, wreathed spirally, and so constituting an open hollow pipe, 

 of a scaly texture, made up of little pipes and bladders, very like the lungs of 

 insects, admitting contraction and dilatation. Whence he concludes the great 

 necessity and use of air and respiration in all those creatures that have even but 

 the least degree of life: which air, he says, is in plants taken in chiefly by the 

 roots out of the earth, there being no such conspicuous air-pipes in the bark or 

 leaves, whereas the roots are exceedingly stored with them. This air, contained 

 in these pipes, and subject to compression and rarefaction, presses by its swelling 

 upon the contiguous woody fibres and their adhering bubbles, and so squeezes 

 out their juice into the neighbouring parts; which being relaxed and emptied, 

 they admit and take in fresh liquor. 



Such plants, that instead of clear liquor contain in their fibrous pipes a coloured 

 juice, have a peculiar vessel, as in the ebulus (dane-wort), fig. 30, and in all 

 lactiferous and resinous plants, fig. 31. And each plant seems to our author to 

 have a peculiar vessel to contain and prepare the last specific nourishment for 



