122 THE PHENOMENON OF 



more returns. The investigation of each link, of each 

 organ of the plant, leads back to the simple cell : the 

 formation of the stem advances by division of a simple 

 apical cell ;* the formation of the leaf starts from a 

 single lateral cell in the vicinity of the apex of the stem ;f 

 every lateral sprout is originally a cell, which, instead of 

 remaining as a mere part of the tissue of the parent 

 sprout, becomes the primary cell of a new developmental 

 series, j To penetrate everywhere to these first rudiments 

 of structure, to follow out from them the course of deve- 

 lopment of the tissues of all parts, and to make out the laws 

 according to which the cell-formation progresses to pro- 

 duce the various arrangements on which the structure of 

 the plant essentially depends, is one of the most difficult, 

 but, at the same time, most profitable tasks, to the accom- 

 plishment of which Nageli, in particular, has quite recently 

 opened the path by accurate and methodical description 

 of the history of the cell-formation and growth of numerous 

 plants belonging to the lower orders of the Vegetable 

 kingdom, from which alone the way can gradually be 

 levelled up to the higher. 



The investigation of cell- formation is no less necessary 



* Definitely demonstrated in the Florideae, e. g., in Polysiphonia and 

 Herposiphonia (Nageli, ' Zeitschrift,' heft 3 and 4, p. 207, t. 6-8) ; Ddesseria 

 hypofflossum (idem, heft 2, p. 121, t.i); Laurencia (Nageli, 'l)ie neueren 

 Algensysteme,' t. 8, f. 4) ; Characese, Musci (Nageli, ' Zeitsclirift,' heft 2, 

 p. 138, t. 4); Equisetaceae (idem, heft 3 and 4, p. 167). If the apical cell 

 divides vertically into two equivalent cells, consequently into two apical cells, 

 dichotomy results (see Dictyota, in Nageli's 'Algensysteme,' t. 5, figs. 12-16), 

 and by rapid repetition a fan-like expansion. Probably the fasciation, as it 

 is termed, of the Phanerogmia, originates in this way. 



'f So at least in the Floridese, Characeee, and Mosses. (See Nageli in the 

 already mentioned places.) 



% See the formation of branches of Echitwmitrion furcalum, in Nageli's 

 ' Zeitschr.,' heft 2, p. 138, t. ii, figs. 1-6. Among; the cases of which we have 

 an exact description, is also the origin of the seed-sprout or ovule of Orchis, 

 which, according to Hofmeister, ('Enstehung des Embryo der Phanerogamen,' 

 1849, p. 1, t. 1) is developed from a single cell of the placenta, which is 

 first divided into two superposed cells, the upper of which by subsequent 

 division forms the cellular coat, the lower the axial row of cells. 



See the treatises relating to this in Nageli's 'Zeitschrift fur wiss. 

 Botanik.' (1845-47), as also his ' Kritik d. neuer. Algensysteme u. Versuch 

 eines eigenen Systems d. Algeu und Florideen,' 1847. 



