18 M. Mohl on the Structure of Annular Vessels. 



Whoever has examined the development of spiral vessels 

 and spiral cellules, and recognised their constant analogy 

 with each other and with the dotted cellules, will not doubt 

 for an instant that he sees in the fibre of spiral vessels, not 

 a particular and independent organism, but rather the se- 

 condary membrane of the vascular utricles, divided in a spi- 

 ral direction into one or more parallel bands. As regards the 

 organization of this pretended fibre, I refer therefore to my 

 work on the organization of the cellular membrane, because 

 all that can be said on the structure of the membrane of the 

 spiral cellule is equally applicable to the wall of the spiral 

 vessel. But as respects what I have to say concerning annu- 

 lar vessels, it is necessary to examine with care some points 

 relative to the spiral fibre. 



In the memoir above quoted I have detailed their striae, 

 their great facility of tearing in a spiral direction, the hollows 

 and furrows lying in a similar direction, and more especially 

 the slits, which entirely penetrate the thickness of the cellular 

 membrane, as the reasons which favour the opinion that the 

 secondary cellular membranes possess a fibrous structure. 

 All these phaenomena, which are so frequently seen on the 

 parts of the cellular membrane situated between the dottings 

 on the cells, are also observable on the fibres of the unrollable 

 spiral vessels ; but are not so often recognised in the latter, 

 either on account of the narrowness of the spiral fibre, or that 

 frequently, even under the highest magnifying powers, the 

 spiral fibre appears homogeneous. When, on the contrary, 

 the fibre is of a considerable width, so that it rather resem- 

 bles a flattened ribbon than a semi-rounded or quadrangular 

 thread, it does not, in most instances, present a homogeneous 

 aspect, but furrows more or less deep are observable in it in 

 the direction of the fibre, either in one row or side by side, and 

 in this last case they give to it a retiform appearance (Plate I. 

 fig. 2. and 3, Commelina tuberosa). In other cases these fur- 

 rows penetrate through the entire thickness of the fibre, which, 

 at different points, is divided into two or more fibres placed 

 side by side. These fibres either take a parallel direction, or 

 the detached fibre at a greater or less distance reunites with 

 the other, or else one of the fibres arising from division, leaving 

 the other part, which continues in its primary direction, rises 

 in a more oblique spiral direction, until it reaches the adjacent 

 coil of the fibre into which it merges. Thus, in short, we 

 observe, that almost all the modifications of form found in the 

 secondary utricular layers result from the close union of all 

 the constituent parts of the fibre, from their more or less de- 



