October, 1913. 



KNOWLEDGE. 



363 



filament too narrow, or the diffraction images of the 

 edges mask all other effects. 



Much of the work in the observation of the living 

 plant cell has been done by N. Gaidukov (see 

 his " Dunkelfeldbeleuchtung" reference at end). 



A few general examples of some of the best 

 objects for observation and the appearance they 

 present may be described, and in many cases the 

 first appearance is sufficiently surprising. One of 

 the most suitable objects for observation is the 

 green alga Spirogyra. A species with fairly thick 

 filaments and a rather loose spiral chloroplast is best, 

 but a close spiral does not prevent good observation, 

 and, in fact, in some cases may be an advantage 

 (Price, S.R. ; see references below). A single fila- 

 ment is mounted in water and covered with a thin 

 cover-slip for observation. Under quite a low power 

 of the microscope of, say, two hundred diameters in 

 good illumination a large number of twinkling points 

 of light with a rapid dancing motion first attract the 

 attention. These are particles which occur in the 

 cell sap and may conveniently be referred to as 

 " sap-particles." They can usually be seen in 

 illumination under high powers, especially with 

 the condenser considerably stopped down. Little 

 attention as yet seems to have been given to these 

 particles, which are apparently widely distributed in 

 plant cells. They seem to increase in number with 

 a lowering of the plant's vitality. 



Under high power, say the three-millimetre apo- 

 chromat of Zeiss, and a six or twelve compensating 

 ocular, much more can be made out. The chloroplast 

 is relatively inconspicuous now, and the protoplast, 

 which lines the wall of the cell and encloses the sap 

 vacuole, is seen to be full of rapidly oscillating and 

 moving particles of a minute size, particles which 

 are not seen in direct illumination. There is some 

 evidence to show that particles of two orders of 

 magnitude are present, the smaller particles being 

 present in the internal and external layers of the 

 protoplast. On focusing in a lower plane — into the 

 vacuole — the sap particles can be seen again, and 

 now they appear rather as minute bubbles of a 

 refracting liquid of a greater order of magnitude 

 •than the protoplasmic particles. In a few cases the 

 nucleus can be seen, appearing almost clear and 

 suspended by protoplasmic fibrils in which are 

 moving particles. 



The whole appearance is certainly very striking 

 and animated, and gives rather a new impression of 

 the great activity of the living cell. 



Incidentally, a dead cell shows none of the 

 protoplasmic movement, and the coagulated proto- 

 plast has quite a different appearance. 



The staminal hairs of Tradescantia have also been 

 observed by Gaidukov and show somewhat the same 

 phenomena. The cell wall is finely striated, how- 

 ever, so that observation is not so easily made. 

 The circulation and streaming of the protoplasm 

 can be well seen. 



The latter is also particulaily well shown by 

 certain cells in the leaf of Elodea, the American 



, water - weed, so common in our waterways. A 

 single leaf is removed and mounted in water. The 

 leaf is only one cell thick at the edge, and, moreover, 

 the chloroplasts are relatively few in these cells. 

 At first only the " sap particles" may be seen, but 

 with careful observation the protoplasm can be 

 observed filled with minute particles, exhibiting a 

 rapid oscillating or Brownian movement. As the 

 leaf warms up the streaming of these particles along 

 the protoplasmic threads and round the cell is clearly 

 seen. After a time a well-marked rotation of the 

 protoplasm is set up, and the minute particles seem 

 to travel along at a great rate. Subsequently 

 enough energy seems to be developed to cause the 

 chloroplasts to move, but these always do so at a 

 slower rate than the small particles. 



Somewhat similar phenomena, . the Brownian 

 movement of the small particles in the protoplasm, 

 and so on, have been described for many other 

 objects ; for example, Mougeotia cells, root-hairs of 

 mustard, yeast cells, multicellular hairs from the 

 tomato plant ; but, as would be expected, there are 

 differences in detail. Yet other cases seem to show 

 little or no movement of the protoplasmic particles. 



The extreme mobility and the great display of 

 activity in some of these plant cells seem at first 

 sight rather surprising and rather militate against 

 some of the older views of the structure of the 

 protoplasm of the living cell. Although the observa- 

 tions yet made are comparatively few — too few to 

 admit of any elaborate theory being postulated — yet 

 some sort of hypothesis is required to explain these 

 phenomena, to be used as a basis for further analysis. 

 The facts as they appear at present seem to agree 

 quite well with the hypothesis that the protoplasm is 

 of the nature of a colloid solution, and in view of 

 recent work on colloids in other directions this view 

 is considerably strengthened. The particles which 

 have been described above are held by Gaidukov to 

 be actual colloid particles, exhibiting the usual 

 Brownian movement when suspended in fluid. The 

 death of the cell results in complete cessation of the 

 movement — the plasma has coagulated. The liquid 

 watery colloidal solution of the living cell is, in the 

 language of the colloid chemist, a hydrosol, and the 

 coagulated mass a hydrogel. The death of the cell 

 is thus a conversion of hydrosol into hydrogel. 



The colloid hypothesis has been further elaborated, 

 but this is not the place to enter into a general 

 discussion of its fuller bearings. It may, however, 

 prove to be a firm stepping-stone leading to a true 

 basis of many of the phenomena connected with the 

 living processes of the cell and with the " life " of 

 the " life-substance " protoplasm. 



The account which has been given is necessarily 

 very superficial and sketchy, but it may in some 

 degree indicate that the method is really a useful 

 one, and one of which a good deal may be expected. 

 The glamour surrounding new methods often results 

 in a gross over-estimate of their application ; but this 

 glamour, let us hope, has partially disappeared in 

 this particular case, although at first it was very 



