ANNALS OF NATURAL HISTORY. 



IX. — On the Discoid Piths of Plants, By Ch. Morren, 

 Professor of Botany in the University of Liege, Member of 

 the Royal Academy of Sciences of Brussels, &c.* 



The immortal Grew could not dissect the wood of the walnut 

 tree (Juglans regia, L.) without being struck with the very 

 singular form of its pith, which is formed of lenticular empty 

 discs and of transversal membranous septa f. Hill, in 1770> 

 who also investigated the structure of woods, observed the 

 same fact, and saw that this form originated exteriorly from a 

 continuous ordinary pith {. Much later (in 1815) M. Mirbel 

 made known a similar organization in the Nyssa aquatica, L. 

 {Nyssa hiflora, Mx.) and in Phytolacca decandra §. In 1827 

 M. DeCandoUe the elder attempted to explain this fact by a 

 rupture, asserting that the pith to assume this form must 

 either have great cells or a tissue not susceptible of extension. 

 The elongation of the young shoots then tore the pith across 

 at the end of the first year, and thence arose both the discoidal 

 cavities, and the transversal discs. This physiologist men- 

 tioned, in addition to the walnut tree, the Jasminum officinaUy 

 as presenting the same structure ||. In 1835 Treviranus ap- 

 pears to adopt the explication of Hill, that the cavities and 

 the discs are derived from a compact pith, and in that Trevi- 

 ranus is perfectly right ; he does not mention any other plant 

 in which this structure might be found If. These remarkable 

 organizations seem to have escaped the scrupulous attention 

 of M. Meyen, who does not notice them in his ^ Physio- 

 logy **.* 



♦ A translation of the MS. original communicated by the Author, 

 t Grew. Anat. Plantarum, 1682. PI. 19. f. 4. 



X Hill. The Construction of Timber from its early growth explained by 

 the Microscope. London, 1770. Tab. X. fig. 1 — 4. 



J Mirbel. Elemens de Physiologie V6g6tale, 1815, vol. i. p. 1 12. 

 II DeCandolle. Organographie, vol. i. p. 167. 

 ^ Treviranus. Physiologie der Gewachse, 1835, vol.i. p. 252. 

 ** Meyen. Physiologie der Pflanzen, 1837, vol. i. p. 377. 



Ann, Nat. Hist, Vol.4. No. 22. Oct, 1839. g 



