ON GROWTH AND EXTENSION IN THE VEGETABLE KINGDOM. 39 



clear spots, or clotted or porous vessels, which, when the clear 

 spots are larger, have been called scalariform or slit vessels, are 

 nevertheless real cells. They are generally longer than the cells 

 of the parenchyma or of the prosenchyma, but the short-articulated 

 vessels (vermicular bodies, or banded vessels) are small enough ; 

 and the woody cells which I have described in my lectures on 

 Phytology, p. 96, and which I might have called cell-vessels, 

 have the ordinary size of cells. But these vessels are very dis- 

 tinct from the cells of the parenchyma and prosenchyma ; they lie 

 together in separate bundles ; they evidently branch out by the 

 separation of single vessels or sm.all bundles, which pass off into 

 other bundles ; thej^ never appear on the surface, but stretch 

 themselves longitudinally through most parts of plants, of w hich 

 they form the basis, the skeleton as it were, and are almost always 

 accompanied by narrow and long cells. The name of cells is 

 very inconvenient for them, for there are porous cells and porous 

 vessels, spiral cells and spiral vessels. It would be as if we were 

 to call all the outer envelopes of the flowers of grasses bracts, 

 which they are indeed really ; but such a generalization of the 

 word would occasion great confusion of language, as the use of 

 the word cells has already produced. Further, spiral and porous 

 vessels are not formed out of cells, of which the intermediate 

 partitions are absorbed or resorbed. I have often observed them 

 in the earliest stage in buds and in roots, and in the latter case 

 figured them several times, and always without any trace of 

 transverse partitions. Cellular tissue in the roots of hyacinths 

 above the root-points has been taken for the commencement of 

 spiral vessels,* which is a mistake; the spiral vessels end long 

 before the root-points, they go directly downwards, and become 

 at length so slender that the spiral thread can scarcely be dis- 

 tinguished. In this excessively fine state no transverse partitions 

 can be seen, and I do not see why we should assume the existence 

 of what no one has as yet seen. As the transverse partitions are 

 not there, they cannot be absorbed. Possibly transparent cellular 

 tissue seen through them may have been mistaken for transverse 

 partitions. A spiral vessel from the upper part of a fibrous hya- 

 cinth root was treated with nitric acid and iodine as above, and 

 by this means the utricle was visible, even in very narrow cells, 

 but the spiral vessel remained uncoloured. 



Spiral vessels and their coating belong therefore in their 

 chemical properties to the same series of parts as the deposits on 

 the inner surface of the cell-walls, and are diflTerent in that 

 respect both from the inner membrane and from the contents of 

 cells, 



* Origin of Spiral Vessels, by Prof. Unger, Linnaea, vol. 15, p. 385, t. 5. 



