ANATOMY OF PLANTS. 179 



only first discovered when the young plant begins to shoot. 

 They are found also in the root, as well as in the stalk : they 

 partly compose the nerves and veins of the leaves and vessels 

 of the corolla : they are found in the stamina, in the pistilla, 

 in the fruit, and also in the funiculus umbilicalis of the seed. 



280. 

 The interior canal of the spiral-vessels, in its natural state, 

 is always found free from M^ater. It is true, that if a piece of 

 wood be dipped in water, this fluid penetrates into the canal. 

 Also, when we permit coloured fluids to flow into the cut 

 branches of plants, these fluids become apparent in the sides 

 of the spiral canals ; but they are also seen, and still more 

 distinctly, in the neighbouring bundles of sap-vessels ; nay, 

 they penetrate in considerable quantity, even into the cellular 

 texture. AVe are not, therefore, entitled, from this entrance 

 of coloured fluids, to conclude respecting the natural con- 

 tents of these canals, because, in general, this penetration of 

 coloured sap does not succeed in a.i uninjured root. 



281. 

 In spirsil canals, which grow rapidly, the fibres are often 

 torn in such a manner, that they fall together in the shape of 

 rings. These ring-shaped vessels, as they have been called, 

 are, therefore, an entirely accidental variety of the primitive 

 form of the spiral vessels ; and this is the more evident, be- 

 cause we find the same vessel in one situation as a spiral 

 canal, and in another as a ring-shaped vessel. This change, 

 besides, shews incontestibly, that the spiral vessels cannot 

 conduct sap, since they are often nothing else but rings at a 

 distance from one another, the circumferences of which are 

 every where and extensively separated. 



282. 



But an important and essential change of the spiral canal 



is that presented by the Vasa scalaria. Under this name 



are included those canals with transverse openings, which do 



not at all shew the spiral winding of the fibres, and which 



M2 



