have found, as Schleiden has observed in cells, that the liquid con- 

 tents become less transparent on account of numbers of the most mi- 

 nute particles, that can be just discerned by the highest magnifying 

 powers, becoming generated in the interior of the vessel, from which 

 it can be observed that fibre, and other deposits in the interior, have 

 their origin ; and it will be my purpose to describe what I have wit- 

 nessed connected with these changes. 



Schleiden imagined that there existed in cells a spiral current be- 

 tween the membrane and the jelly in their interior ; * and mentions 

 that Horkel had seen something analogous in the vessels of Hydro- 

 charts, where a current, he said, exists between the spires of the ves- 

 sel, and that this supposed current determined the direction of the 

 fibre. In fact, to suppose there were such currents in the direction 

 the fibre is deposited, which undoubtedly is most often spiral, what is 

 to become of the fluids in motion when they arrive at the end of their 

 spiral course? It is found that the turns of the spiral are nearly 

 in contact in early life, therefore by what means can the currents be 

 made to keep so distinct a course, and what could give them such a 

 direction ? If there exist any such current, it may account for the 

 formation of a spiral fibre ; but what kind of current could determine 

 the direction of the fibre of a reticulated or dotted duct, or even an 

 annular vessel ? In fact the notion of a current preceding the depo- 

 sition of fibre is, I believe, at most a gratuitous supposition, and in- 

 sufficient to account for the several forms of fibre witnessed in the 

 interior of vessels : and it is nearer the truth to imagine that what can 

 be observed of that law which determines the direction of the fibre in 

 one or more cases, may, with some modifications, serve to explain 

 what happens in all, as it will be attempted to be proved. 



From this conjecture of Schleiden's it is imagined that he had not 

 seen the first commencement of this process, or if so, it is at variance 

 with what I have observed in many cases, and which is particularly 

 evident in the leek and in Polygonum orientate. When the young 

 vessels are recognizedf (which by experience becomes an easy matter, 

 even in parts considerably developed, though not so at first). They 

 appear as pellucid glassy tubes, with a cytoblast in some part of their 

 interior ; earlier than this they are not to be recognized readily from 



* Annales des Sciences Naturelles, Seconde Serie, xi. Botanique, p. 366. 

 fit is necessary in this examination to use the highest powers that optical science 

 has furnished us with, and also to adopt all the means of adjustment and illumination 

 that are found requisite for obtaining the most perfect definition ; and especially mak- 

 ing the observations by daylight. 



