Prof. C. Morren on the discoid Piths of Plants. 83 



The cells (fig. 9.) remain the same, cubic, somewhat transpa- 

 rent, and forming two or three layers in the centre with a 

 massive root (A, fig. 9.) either surrounding the disc or di- 

 vided. Some cells have their crystalline calculi also in the 

 centre, but the greater part of such crystals are scattered 

 outside the cells and fall off when the branch of the walnut 

 tree is opened. 



We know that this tree diffuses a powerful odour, owing to 

 the evaporation of a very subtle volatile matter, which has a 

 deleterious effect upon some persons, who suffer from head- 

 ache when they sleep under the tree or handle any part of it. 

 In the numerous dissections which I have made of the plant 

 in my study I have felt this effect myself. All the parts of 

 the plant are full of this empyreumatic matter. We know 

 that in Circassia the tree is bored in the spring to draw off a 

 liquid matter which coagulates and which the Circassians use 

 in debilitant diseases and in affections of the lungs*. 



I was very much surprised to find a resinous substance in 

 the old pith of this tree, which accumulates on the discs, 

 and there forms very singular tear-shaped masses (fig. 9. c). 

 These yellow masses have a multitude of different peculiar 

 figures, but in general they are tuberosities supported by feet, 

 the parts of which radiate in order to place and attach them- 

 selves on the medullary discs. On the tuberosities there are 

 projections of tissue also radiating, and all the tissue itself of 

 these masses is as it were granulated with a tendency to irradi- 

 ation. This is explained at fig. 9. in c, where I have drawn 

 one of these masses with two feet. 



The existence of this substance in this place would lead us 

 to think that in the exhaustion of the pith by the bud all the 

 substances are not equally absorbed, and that some of them 

 remain in the exhausted pith, which would then become not 

 only an alimentary organ of the bud, a reservoir of air, but 

 also a place of deposit, or, if we choose, a species of cloaca 

 where substances henceforward useless accumulate. I know 

 not whether pith has as yet been considered in this latter 

 point of view, but the inorganic crystals accumulated in some 



* See the excellent work of Dr. Lindley, Flora Medica. London, 1838, 

 p. 308. 



