THE TEGETxlBLE CELL. 3 



organs, to <assniiie forms which would be foreign to it under eon- 

 <iitions of free, unrestrained development. 



The sphere must be regarded as the fundamental form, in w^hich 

 every freely developed cell first appears. Although this form oc- 

 curs not unfrequently with great regularity in very young cells, 

 this is more rarely the case in full-grown cells. For in most in- 

 stances the growth of cells is by no means uniform ; sometimes one 

 diameter remains short and the cell assumes the form of a flattened 

 ellipsoid ; but far more often one of the diameters becomes more 

 or less elongated, and the cell passes into the form of an elon- 

 gated ellipsoid, or, by farther extension, into that of a cylinder. 

 Roundish forms are found more or less regularly developed in many 

 lower Algge, €,g,^ in Protococcus, in the yeast plant, in completely 

 or almost ^wholly isolated cells of higher plants, as in spores and 

 pollen-grains, in the knob-shaped ends of many hairs of plants, &;c. 

 The cyUndrical or attenuated conical forms are likewise frequent in 

 the lower orders of the vegetable kingdom, in hairs, and the like. 



The frequently occurring foi^m of the elongated ellipsoid, and 

 still more the cylindrical shape, point to the innate tendency of 

 the vegetable cell towards an unequal growth, in which an oppo- 

 sition manifests itself between the longitudinal axis and the 

 transverse axes, between the upper and lower ends, and the 

 lateral faces of the cell ; but in many other cases a still greater 

 deviation from the primary form is met with, where particu- 

 lar points exhibit an isolated growth, giving rise to papillary 

 elevations and gradual development of these into cylindrical pro- 

 cesses, and thus to a ramification of the cell. The 

 phenomenon is very common ; it occurs, for instance, ^ig. i. 

 in the formation of the pollen-tubes upon the stigma, 

 in the germination of most spores, and in the most 

 striking degree in many Algm. In these last the 

 ramifications produced at the lower end of the cell 

 fi-equently form a contrast to the upper end, since 

 they fulfil the functions of root fibrils, e. gr., in Botry- 

 diuTTh (fig. 1), in germinating Oonfervce, &c., while the 

 protrusions sprouting out from the upper end form 

 the foundation of abundant, often very regular, rami- 

 fications of the plant, e, (/., in Vaubcheria^ Bryopsis, 

 &c. This phenomenon is seen most distinctly in uni- 

 cellular Algae, as in the genera just named ; but in 

 most cases this process of ramification is combined 

 with cell-division, which renders the detection of it 

 difiicult, and the uni-cellular becomes converted into a ^ ^ ,. 

 many-celled plant, e,g,, m Gonferva glomerata (pL 1, utum. 

 figs. 1 — 6), 



Those cells which have grown together with other cells or with 

 vascular utricles, into a tissue, exhibit much slighter differences 

 of form than the freely developed cells. It is true that in this 



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