VII] OF CELL-PARTITIONS 305 



years later, Sachs formulated his rule, or principle, of " rectangular 

 section," declaring that in all tissues, however complex, the 

 cell-walls cut one another (at the time of their formation) at right 

 andes*. Years before, Schwendener had found, in the final 

 results of cell-division, a universal system of "orthogonal tra- 

 jectoriest"; and this idea Sachs further developed, introducing 

 complicated systems of confocal ellipses and hyperbolae, and 

 distinguishing between periclinal walls, whose curves approximate 

 to the peripheral contours, radial partitions, which cut these at 

 an angle of 90°, and finally antichnes, which stand at right angles 

 bo the other two. 



Reinke, in 1880, was the first to throw some doubt upon this 

 explanation. He pointed out various cases where the angle was 

 not a right angle, but was very definitely an acute one; and 

 he saw, apparently, in the more common rectangular symmetry 

 merely what he calls a necessary, but secondary, result of growth J. 



Within the next few years, a number of botanical writers were 

 content to point out further exceptions to Sachs's Ilule§; and in 

 some cases to show that the curvatures of the partition- walls, 

 especially such cases of lenticular curvature as we have described, 

 were by no means accounted for by either Hofmeister or Sachs ; 

 while within the same period, Sachs himself, and also Rauber, 

 attempted to extend the main generalisation to animal tissues ||. 



While these writers regarded the form and arrangement of the 

 cell-walls as a biological phenomenon, with little if any direct 

 relation to ordinary physical laws, or with but a vague reference 

 to " mechanical conditions," the physical side of the case was 

 soon urged by others, with more or less force and cogency. Indeed 

 the general resemblance between a cellular tissue and a "froth"' 



* Sachs, Ueber die Anordnung der Zellen in jiingsten Pflanzentheilen, Verh. 

 pkys. med. Ges. Wurzburg, xi, pp. 219-242, 1877 ; Uteber Zellenanordnung und 

 Wachsthiim, ibid, xii, 1878; Ueber die durch Wachsthum bedingte Verschiebung 

 kleinster Theilchen in trajectorischen Curven, Monatsber. k. Akad. Wiss. Berlin, 

 1880; Physiology of Plants, chap, xxvii, pp. 431-459, Oxford, 1887. 



t Schwendener, Ueber den Bau und das Wachsthum des Flechtenthallus, 

 Naturf. Ges. Zurich, Febr. 1860, pp. 272-296. 



f Reinke, Lehrbuch der Botanik, 1880, p. 519. 



§ Cf. Leitgeb, Uriters. ilber die Lebermoose, ii, p. 4, Graz, 1881. 



I! Rauber, Neue Grundlegungen zur Kenntniss der Zelle, Mar ph. Jahrb. vnr, 

 pp. 279, 334, 1882. 



T. G. 20 



