8 MORPHOLOGY OF THE CELL. 



the materi^J required is always afforded by protoplasm already present; the newly 

 constituted protoplasmic body clothes itself, sooner or later, with a new cell-wall. 

 This is the only process common to all reconstruction of cells. A description 

 which goes more into detail requires a distinction to be at once drawn between 

 different cases, or we shall be led into erroneous generalizations, since there is 

 great variety in the mode in which new cells are formed. 



It appears to me convenient and natural to distinguish three principal types : — 

 ( I ) The Renewal or Rejuvenescence of a Cell ; i. e. the- formation of one new cell 

 from the whole of the protoplasm of a cell already in existence; (2) The Conju- 

 gation or Coalescence of two (or more) protoplasmic bodies in the formation of a 

 Cell ; (3) The Multiplication of a Cell by the formation of two or more protoplasmic 

 bodies out of one. Each of these types shows a series of variations and transidons 

 into the others. Great diversity arises, especially in the multiplicadon of cells. 

 Two cases are here to be distinguished first of all, according as a part only of the 

 protoplasm of the mother-cell is applied to the formation of the new cells (Free 

 Cell-formation), or as the whole mass passes over into the daughter-cells (Division). 

 The last, by far the most common case, again exhibits variations, according as the 

 masses of protoplasm, w-hich become separated and then collect around new centres, 

 expel water and contract, and become globular, or not, and according as the 

 cell-wall is secreted during the division or only after the complete formadon of the 

 new cell, and even after the appearance of cell-sap and nuclei. 



In the course of the vegetation of a plant, different forms of cell-formation 

 are brought into play. On Cell-division depends the formation of the vegetative 

 parts of the plant, the production of the Cell-tissue ; Free Cell-formation occurs in 

 the production of the ascospores of Fungi and Lichens, and in the embryo-sac of 

 Phanerogams ; Cell-formation by Conjugation is limited, in its typical form, to 

 single groups of Algae and Fungi for the purpose of reproducdon ; the Renewal or 

 Rejuvenescence of Cells is found in the formation of a single swarm-spore out of 

 the whole contents of a vegetadve cell in many Algae ; and analogous phenomena 

 occur in the sexual reproduction of Cryptogams. 



In what follows I purpose to give a summary of the different kinds of cell-forma- 

 tion according to the principles already indicated. The brevity required in an 

 introductory treatise will be my excuse if I omit the details necessary for a more 

 accurate knowledge. 



A. Cell-formation by Renewal or Rejuvenescence of a Cell. — A good ex- 

 ample is afforded in the formation of the swarm-spores of Stigeoclonium insigne (Fig. 3, 



Botan. Zeitung, 1844, p. 273. — Nageli, Zeitschrift fiir wiss. Botanik, I. 1844, p. 34, III, IV, 1846, p. 50. 

 — A. Braun, Verjiingung in der Natur, Freiburg 1850, p. 129 et seq. — Hofmeister, Vergleichende 

 Unsersuchungen iiber die Embryobildung der Kryptog. u. Conif., Leipzig 1851.— De Bary, Untersuch- 

 ungen uber die Familie der Conjugaten, Leipzig 1858. — Nageli, Pflanzenphys, Untersuchungen, 

 Heft I.— Pringsheim, Jahrb. fiir wiss. Botanik, I. 1858, pp. i, 284, 11. p, i.— Hofmeister, Lehre von 

 der Pflanzenzelle, Leipzig 1867. [Schleiden's Contributions to Phylogenesis are in Taylor's gcient. 

 Mem., vol. II. pp. 281-312, and Sydenham Society, 1847; Braun's Rejuvenescence was published 

 by the Ray Society in Bot. and Phys. Mem. 1853; and Nageli on Vegetable Cells by the same 

 Society in their Reports and Papers on Botany, 1845 and 1849.] 



