M. Mohl 0)1 the Structure of Annular Vessels. 19 



cided separation into isolated threads, from deviations in the 

 course of these from that of the main-thready or from a reticu- 

 lated union of the isolated threads. 



The direction in which the spiral fibre is wound has, indeed, 

 no direct connexion with the organization of the vessel ; never- 

 theless I think it necessarj'- to make some remarks on this sub- 

 ject, because several erroneous statements, partly founded upon 

 an imperfect knowledge of the spiral, have been advanced by 

 some authors. I have elsewhere said that the great majority 

 of spiral vessels were wound to the right ; that is, the volution 

 of the fibre is such, that, to an observer placed in the axis of 

 the cylinder around which the spiral line rises, the fibre ap- 

 pears to mount from left to right, as shown in the vessel repre- 

 sented at figure 5. Like most other phytotomists, Schleiden 

 says that the spiral fibre is wound sometimes to the right, 

 sometimes to the left ; and he thinks it possible to admit pro- 

 visionally, as a general rule, that in spiral organizations " co- 

 temporaneously" developed, those which are situated imme- 

 diately side by side in the direction of the radius have similar 

 directions [homodi'Gmes), whilst those placed side by side in 

 directions parallel to the periphery have different directions 

 {heterodromes) ; and in proof of this law he relies on the con- 

 stant crossing of the pore-like fissures in contiguous parenchy- 

 matous and ligneous cellules when obsened in sections made 

 parallel to the medullary rays. I must confess my inability to 

 conceive how Dr. Schleiden can allege the crossing of the porous 

 fissures in support of the volution of the fibres in different di- 

 rections, since it proves quite the contran,'. This crossing is 

 seen when two vessels or cellules furnished with pores are su- 

 perposed, and the adjacent parietes wound in opposite direc- 

 tions ; but it is evident that this last case is only possible when 

 the winding in the two vessels is homodromous ^. It is quite 

 true that we generally see the porous fissures crossing each 

 other in a section parallel with the medullary rays ; which 

 proves that the different layers of cells visible in such a section 

 and placed one under the other, are wound in a homodromous 

 direction ; but as at the same time the cells of every such 

 layer are homodromous with each other, it clearly follows that, 

 generally speaking, all the cells of a plant are homodromous ; 

 and this, in fact, will be found to be so on an examination of 

 difi^erent sections of the same plant. 



Without doubt spiral vessels exist which are wound to the 

 left; but although I have latterly found them more fre- 

 quently than formerly, I must still persist in asserting them 



* [This illustration may be easily verified by applying two quills toge- 

 ther, with equidistant homodromous or heterodromous spirals scratched upon 

 them. — £d.] 



C 2 



