the Development of the Organic Cell. 5 



that, for a long time, they have been looked upon, as some even 

 now are, as solid unorganized particles ; whilst others have such 

 thin walls that they have either been overlooked, or else regarded 

 as cavities in the less transparent and denser cell-contents. 



Such gaps in our knowledge of the structure of the cell 

 render the right apprehension of its functions impossible, as is 

 shown, for example, among other problems, by that of the 

 phenomenon of the circulation of the sap, which has been so 

 much canvassed, and regarding which a distinguished physiolo- 

 gist has recently expressed himself in a manner which can only 

 be explained by a misapprehension of the anatomical nature of 

 the cell. 



In my 'Histological Researches' (p. 61) I have detailed my 

 views I'especting the general cause of the circulation of the juices 

 within cells ; and I will now describe the structure of the hairs 

 of Urtica, which explains the apparently wonderful circulation 

 within their large cell-cavities. In PI. I. figs. 1 & 3, is repre- 

 sented a large hair of Urtica urens, with its cui-ved and rounded 

 extremity. The large hair-cell, under a low magnifying power, 

 appears filled with a colourless though somewhat turbid liquid, 

 and has an inferior rounded extremity surrounded by an epi- 

 dermic layer of cells. On the wall (as in fig. 1) or in the me- 

 dian line (in fig. 2) of the portion of the hair-cell which pro- 

 jects freely from the cup-like base is seen a large nuclear cell 

 filled with a whitish mucilaginous substance and a nuclear ve- 

 sicle. At times, particularly in fully grown stages, this organ 

 is concealed by the cellular envelope at their base. 



By rather stronger magnifying powers, it becomes evident 

 that this nucleus is the central point of currents of a turbid 

 finely granidar fluid, which spreads itself more or less com- 

 pletely over the inner surface of the thick wall of the hair. By 

 a little attention, it is further seen that the streams which pass 

 across the interior of the cell are not all thread-like, as appears 

 at first sight, or at least are not constantly so, but in part 

 coalesce into a thin layer of fluid, which here and there, espe- 

 cially in the lower portion of the hair, gets collected in the form 

 of a thicker column, usually more rapid in its course. The 

 fibre-like stream is also as little constant in character as the 

 wider but thinner current : at times it flows rapidly, at others 

 slowly; at one time the tenacious-looking granular fluid collects 

 in one place, at another it breaks away from the locality in 

 which it has been confined, to extend to other parts, and thereby 

 sufi"ers some change in its direction. A rapid current is esta- 

 blished especially after the hair has been placed in water under 

 the microscope for a short time, as from two to three minutes, 

 — a circumstance, no doubt, due to the diff"usion of the water. 



