Prof. C. Morren on the discoid Piths of Plants. 85 



its circumference ; in a vertical section of the stalk the discs 

 remain without colour, but their roots become blue. Figure 

 10. represents this. The cells a. contain some fecule b, at- 

 tached to their partition ; the cells c, d. have their fecule in a 

 mass in the centre of their cavity ; and the cells of the discs 

 e,f, g. have no longer any fecule at all. Here we may per- 

 ceive, and there is no better way, the absorption of this nu- 

 tritive substance, after which the pith dries up and separates 

 its layers of cellules. 



In fact, in Jasminum fruticans, where the pith is like a lace- 

 net, the discs are extremely fine ; which arises from their being 

 formed by a single plane of very small cells. There is then not 

 the slightest occasion, as has been supposed, for the cells to 

 be great in order for the pith to slit into discs. Here they 

 are of the smallest size. 



In Jasminum officinale the discs are also so minute that 

 the cells sometimes separate, and thus leave real holes by 

 which the cavities communicate with one another. This dis- 

 position allows the pith of this plant to be injected, especially 

 with wax made red with cinnabar, and when cold it is one of 

 the most beautiful preparations of vegetable anatomy. I have 

 some stems thus preserved in the museum at Liege. 



The Phytolacca decandra presents enormous lenticular 

 cavities, as figure 12. shows (e.), the intermediate discs of 

 which are also very thick. The tissue which forms them is 

 a prismenchyma with very large cells, which is the opposite 

 of the jessamine, and proves that the size of these bodies has 

 nothing to do with the separation of the pith into discs. 

 These cells have numerous clusters of acicular crystals be- 

 tween them [dy fig. 13.), and in the cells themselves very small 

 globules are seen. The membranes are very fuU of folds, but 

 here also, when we dissect with care, we find no broken cells 

 nor a true rent. 



It is proved then, by these numerous examples, that a dis- 

 organization of tissue does not exist in the formation of these 

 cells. The pith is exhausted by furnishing the bud with its fe- 

 cule, as does the cotyledon ; but if this then changes into a leaf 

 in the epigeous plants, by turning its diachyma green, the pith 

 on the contrary from being green becomes blanched and com- 



