50 ANATOMY AND PHYSIOLOGY OF 



from tlie globuleb of tlie milk-sap; from cavities appealing iu a homo- 

 geiieons cambium, &c. Brisseau de Mirlbel was the only one who sought 

 to solve the problem of cell-formation by careful observation of the deve- 

 lopment of Marchantia^ but he did not succeed in finding out the mode 

 of development of the single cell; he believed that he discovered three 

 modes of formation of cells : a, between other cells {developpemeQit inter-u- 

 tricukdre) ; h, on the surface of other cells (dSvel super-utriculaire) ; c, in 

 the cavity of other cells {devel. intTa-utriculaire). But all more recent 

 observations speak decidedly against the existence of the first two modes 

 of development described by Mirbel. It is true that Kiitzing (" Phyco- 

 logia generalisp^ 64) has assumed the formation of cells in the intercel- 

 lular substance, and, in like manner, linger (" Gmnch. der Anatomie;' 40) 

 attributes this process to the Phanerogamia. ]N'either of them, however, 

 have any adequate evidence for the support of their views. In the dis- 

 sertation just spoken of, I sought to demonstrate in the Cryptogamie 

 water-plants, that the earfier notion of the necessity of cells originating 

 under the form of very small vesicles was false, and that division of the 

 cells takes place by the formation of partitions, which cut off the contents 

 of the parent-cells into separate portions ; but it was not mitil I had 

 discovered the primordial utricle that I was able to trace accurately the 

 pi'ocesses in the formation of this septum. (See the revised edition of this 

 paper in my " VermiscM, /Schrifi" 1845.) Before this had happened 

 Schleiden ( "Beitrdge zur Fhytogenesis^' in '^ Mullet's ArcMv" 1838, TransL 

 in " Taylor's Scientific Memoirs," vol. ii.) had discovered the free cell- for- 

 mation, and declared it to be the sole mode of formation of cells, whereby 

 the whole theory of the development of cells was pushed into a false direc- 

 tion, from which it has been chiefly brought back into the right path by 

 linger and ISTageli, who demonstrated the great prevalence of the procesFi 

 of cell-division, 



a. Division of the Celt 



The multiplication of cells hj division commences by changes 

 undergone by the primordial utricle of the dividing cell, in conse- 

 quence of •which partitions are developed, growing gradually 

 inwards from the periphery of the cell, and dividing the cavity of 

 the cell into two or more separate compartments. This process 

 is preceded in almost all cases by a formation of as many nuclei as 

 there are to be compartments in the mother-cell ; in rare cases this 

 process does not occur, and the changes of the cell-contents are 

 limited to the phenomena wliich present themselves in the pri- 

 mordial utricle. 



I investigated the second simple process chiefly in Gofiferva 

 glomerata (" Verm, Schrifif' 628). This Conferva (pi. 1, fig. 1) 

 exhibits growth and cell-multiplication at two places. The prin- 

 cipal trunk of it consists of a row of cylindrical cells of pretty 

 nearly equal length ; the end cell of these (a) becomes elongated 

 to twice the length of a cell (fig. 2), and then divided in the 

 middle (fig, 2 a), by a cross-partition, into two cells of the usual 

 length, of which the lower remains unaltered, while the upper 

 undergoes the same changes as the previous terminal cell, &c. 



