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



of them, and the deposition of the resinous matter, which we 

 have seen exists in the pith of walnut trees, authorizes us to 

 think thus. 



I said above that nothing was more unequal than the dis- 

 tribution of the discoid piths in the different species of the 

 same genus. If the examples which I have quoted are not 

 sufficient, I will take the genus Jasminum, where Jasminum 

 azoricum, L., offers a dense continuous pith filled with juice, 

 and Jasminum officinale a discoid pith. That of the last spe- 

 cies being sufficiently known, I have preferred, for multiply- 

 ing examples and consequently our knowledge, to investigate 

 the Jasminum fruticans, L., whose beautiful little pith offers 

 the most delicate diaphragms that can be seen : we might 

 suppose it to be a section of some vein with valves, when it is 

 cut across ; but this pith is one of the most interesting for ex- 

 hibiting the real object which nature had in emptying the 

 piths in favour of the bud ; for here the phenomena of nutri- 

 tion are so capable of appreciation, that it is one of the best 

 examples to give in a course of vegetable physiology. 

 I stop then to examine the Jasminum fruticans. 

 If Ave take the top of the flowering stalk of this species, we 

 find a continuous pith, the nearly cubic cells of which present 

 a great quantity of little granules. If tincture of iodine is 

 passed over a section of this stalk all the pith and cellular en- 

 velope instantly become blue. The fact is that both are filled 

 with fecule, these granules being nothing else. At that time 

 the two reservoirs of fecule, stained blue by iodine, are dis- 

 tinctly separated by the fibres of the ligneous system, which 

 do not become blue. 



If a subjacent internode is taken where the medullary discs 

 are already formed, and if the preparation is passed through 

 tincture of iodine, we first see the cellular envelope become 

 blue, then two blue lines within the fibrous system ending at 

 the discs of the pith, which are of a paler blue. At this period 

 the fecule in fact still exists throughout the cellular system, 

 but in a smaller quantity in the centre of the pith, w 7 here it 

 has been absorbed to the advantage of the buds. 



Lastly, if we take an older internode, the iodine only co- 

 lours the exterior system, and two lines of the pith, those of 



