VII] OF CELL-PARTITIONS 481 



partition capable of doing so. Ten years later, Sachs formulated 

 his rule of "rectangular section," declaring that in all tissues, 

 however complex, the cell-walls cut one another (at the time of 

 their formation) at right angles*. Years before, Schwendenlfer had 

 found in the final results of cell-division a universal system of 

 "orthogonal trajectoriesf; and this idea Sachs further developed, 

 introducing complicated systems of confocal elhpses and hyperbolae, 

 and distinguishing between pericHnal walls whose curves approxi- 

 mate to the peripheral contours, radial partitions which cut these 

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

 to the other two. 



Reinke (in 1880) was the first to throw doubt upon this explana- 

 tion. He pointed out cases where the angle was not a right angle, 

 but very definitely an acute one; and he saw in the commoner 

 rectangular symmetry merely what he called a necessary, but 

 secondary, result of growth {. 



Within the next few years a number of botanical writers were 

 content to point out further exceptions to Sachs's rule§, 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^. 

 The simple fact is that Sachs's rule is limited to those many 

 caaes where one cell-wall grows stiff or solid before another 



* Sachs, Ueber die Anordnung d. Zellen in jiingsten Pflanzentheilen, Verh. pkys.- 

 med. Gesellsch. Wurzhurg, xi, pp. 219-242, 1877; Ueber Zellenanordnung u. 

 Waehstum, ibid, xii, 1878; cf. Arb. bot. Inst. Wurzburg, ii, 1882; Ueber die durch 

 Wachstum bedingte Verschiebung kleinster Theilchen in trajeetorisehen Curven, 

 Monatsb. k. Akad. Wiss. Berlin, 1880; Physiology of Plants, chap, xxvii, Oxford, 

 1887. 



t Schwendener, Bau u. Wachstum des Flechtenthallus, Naturf. Gesellsch. Zurich, 

 1,860," pp. 272-296. 



J Reinke, Lehrbuch d. Botanik, 1880, p. 519; Kienitz-Gerloff, Botan. 7Ag. 1878, 

 p. 58, had already shewn some exceptions "to Sachs's rules, and ascribed them, 

 vaguely, to "heredity." It was a time when heredity overruled everything, and 

 when Sachs himself spoke of the difficulty of demonstrating the causes of any 

 morphological phenomenon in any other way than "genetically": Textbook. 1882, 

 p. 201. 



§ E.g., Leitgeb, V niersuchungen iiber die Lebermoose, ii, p. 4, Graz, 1881. 



•i Rauber, Neue Grundlegungen zur Kenntniss der Zelle, Morvhol. Jahrb. viii, 

 pp. 279, 334, 1882. 



