20 M. Mohl on the Sfruchire of Annular Vessels. 



to be much rarer than those wound to the right, and that they 

 should rather be considered as exceptions to the rule, since, 

 in most plants, we find a hundred spiral vessels wound to the 

 right for a single one wound to the left. Doubtless it is true 

 that these proportions vary in different plants, and I cannot 

 yet say whether the finding in them more frequently spiral 

 vessels wound to the left be a fact pecuhar to certain species 

 or only to certain individuals : generally they are, as I have 

 said, wound to the right. The volution to the right or to the 

 left, in spiral vessels, is quite independent of the organization 

 of the surrounding parts, as is proved by the fact that, in cer- 

 tain cases, not only the fibres of two superposed utricles of 

 the same vessel are wound in opposite directions, but some- 

 times even in the same vascular utricle (as 1 have seen in 

 the Gourd) the parts of the spiral fibi-e separated from each 

 other by rings are wound in an opposite direction (Plate I. 

 fig. 9). 



When we examine the fibre of the perfectly developed an- 

 nular vessel (for which researches I have been accustomed to 

 use the Commelina tuberosa), we find its organization per- 

 fectly analogous to that of the spiral fibre, in the rings being 

 composed sometimes of an apparently homogeneous sub- 

 stance, and sometimes exhibiting traces of a determinate 

 structure. 



In the broad fibres, as in the Commelina tuberosa, the fibre 

 frequently exhibits a great number of shallow linear furrows 

 or perfect fissures, forming a net-work of very narrow and 

 elongated meshes (fig. 1, 3). More frequently still these fis- 

 sures are found in an uninterrupted line in the medial line of 

 the fibre, or they become confluent, and thus divide the ring 

 into two superposed rings (fig. 4 a, a, Commelina tuberosa). 

 When this latter division takes place, it generally recurs on 

 every ring of a vessel. Frequently, however, this does not 

 occur; but divided and undivided rings alternate in an irre- 

 gular manner, the undivided rings being sometimes of equal 

 size, sometimes of half the size of the divided rings, and 

 sometimes of a size very inconsiderable in comparison with the 

 divided rings (Plate I. fig. 1, Commelina tuberosa). 



The direction of this line of division is parallel to the lateral 

 edges of the ring, so that, by this fissure, the ring is divided into 

 two superposed rings, which sometimes touch and sometimes 

 are placed at a little distance from each other. According to 

 Schleiden, this line of division proceeds from the coils of the 

 spiral fibre being more or less completely soldered together, 

 and always in pairs. We easily perceive that, in this case, the 

 line of partition should be directed spirally from one edge of 

 the ring towards the other, and that it should not be parallel 



