MICROSCOPIC STRUCTURE OF PHANEROGAMIC PLANTS. 359 



cms to use a l-8th inch Objective, with an Achromatic Condenser having 

 a series of diaphragms. The nature of the movement in the hairs of dif- 

 ferent species is far from being uniform. In some instances, the currents 

 pass in single lines along the entire length of the cells, t as in the hairs 

 from the filaments of the Tradescantia virginica, or Virginian Spider- 

 wort (Fig. 240, A); in others there are several such currents which retain 

 their distinctness, as in the jointed hairs of the calyx of the same plant 

 (B); in others, again, the streams coalesce into a network, the reticula- 

 tions of which change their position at short intervals, as in the hairs of 

 Glaucium luteum; whilst there are cases in which the current flows in a 

 sluggish uniformly-moving sheet or layer. Where several distinct cur- 

 rents exist in one cell, they are all found to have one common point of 

 departure and return, namely, the nucleus (B, #); from which it seems 

 fairly to be inferred that this body is the centre of the vital activity of 

 the cell. Mr. Wenham states that in all cases in which the cyclosis is 

 seen in the hairs of a plant, the cells of the cuticle also display it, pro- 

 vided that their walls are not so opaque or so strongly marked as to pre- 

 vent the movement from being distinguished. The cuticle may be most 

 readily torn off from the stalk or the midrib of the leaf; and must then 

 be examined as speedily as possible, since it loses its vitality when thus 

 detached, much sooner than do the hairs. Even when no obvious move- 

 ment of particles is to be seen, the existence of a cyclosis may be con- 

 cluded from the peculiar arrangement of the molecules of the protoplasm, 

 which are remarkable for their high refractive power, and which when 

 arranged in a i moving-train,' appear as bright lines across the cell; and 

 these lines, on being carefully watched, are seen to alter their relative 

 positions. The leaf of the common Platitago (Plantain or Dock) fur- 

 nishes an excellent example of cyclosis; the movement being distinguish- 

 able at the same time both in the cells and in the hairs of the cuticle torn 

 from its stalk or midrib. It is a curious circumstance that when a plant 

 which exhibits the cyclosis is kept in a cold dark place for one or two 

 days, not only is the movement suspended, but the moving particles col- 

 lect together in little heaps, which are broken-up again by the separate 

 motion of their particles, when the stimulus of light and warmth occa- 

 sions a renewal of the activity. It is well to collect the specimens about 

 midday, that being the time when the rotation is most active, and the 

 movement is usually quickened by artificial warmth, which, indeed, is a 

 necessary condition in some instances to its being seen at all. The most 

 convenient method of applying this warmth, while the object is on the 

 stage of the Microscope, is to blow a stream of air upon the thin-glass 

 cover, through a glass or metal tube previously heated in a spirit-lamp. 



356. The walls of the cells of plants are frequently thickened by inter- 

 nal deposits, which may present very different appearances according to 

 the manner in which they are arranged. In its simplest condition, such 

 a deposit forms a thin uniform layer over the whole internal surface of 

 the cellulose-wall, scarcely detracting at all from its transparence, and 

 chiefly distinguishable by the ' dotted ' appearance which the membrane 

 then presents (Fig. 236, A). These dots, however, are not pores, as 

 their aspect might naturally suggest, but are merely points at which the 

 deposit is wanting, so that the original cell-wall there remains unthick- 

 ened. A more complete consolidation of Cellular tissue is effected by 

 deposits of sclerogen (a substance which, when separated from the resi- 

 nous and other matters that are commonly associated with it, is found 

 to be allied in chemical composition to cellulose) in successive layers, one 



