244 MULTIPLICATION OF UNICELLULAR PLANTS. 



ture or in actions between their component cells; each one of 

 these being a repetition of the rest, and no relation of mutual 

 dependence existing among them. — All such organisms may well 

 be included under the general term of Protophytes, by which it 

 is convenient to designate these primitive or elementary forms of 

 Vegetation ; and we shall now enter, in such detail as the nature 

 of the present Treatise allows, into the history of those forms of 

 the group which present most of interest to the Microscopist, or 

 which best serve to illustrate the general doctrines of Physiology. 



185. The life-history of one of these Unicellular Plants, in its 

 most simple form, can scarcely be better exemplified than in the 

 Palmoghea macrococca (Kiitzing) ; one of those humble kinds of 

 vegetation which spreads itself as a green slime over damp stones, 

 walls, &c. When this slime is examined with the microscope, it is 

 found to consist of a multitude of green Cells (Plate viii. Fig. 1, a), 

 each surrounded by a gelatinous envelope ; the Cell, which does not 

 seem to have any distinct membranous wall, is filled with granular 

 particles of a green colour ; and a nucleus, or more solid aggregation 

 which appears to be the centre of the vital activity of the cell, may 

 sometimes be distinguished through the midst of these. When 

 treated with tincture of iodine, however, the green contents of the 

 cell are turned to a brownish hue, and a dark-brown nucleus (g) is 

 distinctly shown. Other cells are seen (b), which are considerably 

 elongated, some of them beginning to present a sort of hour-glass 

 contraction across the middle ; in these is commencing that curious 

 multiplication by binary subdivision, which is the ordinary mode 

 of increase throughout the Vegetable kingdom ; and when cells in 

 this condition are treated with tincture of iodine, the nucleus is 

 seen to be undergoing the like elongation and constriction (h). A 

 more advanced state of the process of subdivision is seen at c, in 

 which the constriction has proceeded to the extent of completely 

 cutting-off the two halves of the cell, as well as of the nucleus (i), 

 from each other, though they still remain in mutual contact ; but 

 in a yet later stage they are found detached from each other (d), 

 though still included within the same gelatinous envelope. Each 

 new cell then begins to secrete its own gelatinous envelope, so that, 

 by its intervention, the two are usually soon separated from 

 one an other (e). Sometimes, however, this is not the case ; the 

 process of subdivision being quickly repeated before there is time 

 for the production of the gelatinous envelope, so that a series of 

 cells (p) hanging-on one to another is produced. — There appears 

 to be no definite limit to this kind of multiplication ; and exten- 

 sive areas may be quickly covered, in circumstances favourable to 

 the growth of the plant, by the products of the duplicative sub- 

 division of one Primordial Cell. This, however, is simply an act 

 of Growth, precisely analogous to that by which any one of the 

 higher forms of Vegetation extends itself, and differing only in this, 

 that the cells produced by each act of subdivision in these simplest 



