On the Multiplication of Vegetable Cells by Division. 441 



forward in the preceding pages to the investigations of other in- 

 quirers. 



In the first place, with regard to the action of sulphuric acid 

 and iodine upon the various membranes, H. von Mohl* has shown 

 that this depends more upon the age of the structure than any- 

 thing else. He finds that these reagents produce the blue colour 

 in young cell-membrane, and that the older structures which are 

 usually coloured brown, are brought into a condition to acquire 

 the blue tint with iodine by boiling in nitric acid or solution of 

 potash ; and this without destroying the membrane, at all events 

 without converting it into starch, since it remains insoluble in 

 boiling water. He finds solution of potash produce the effect 

 best in epidermal structures; nitric acid in the ligneous tissues. 

 It is uncertain whether this altered condition of old tissues de- 

 pends on spontaneous alteration or the penetration of the tissue 

 by new substances. Ungerf also states that these structures 

 which are usually coloured brown by iodine may be made to ac- 

 quire the blue colour by boiling in concentrated sulphuric acid. 

 These observations show that mere chemical reaction is not suffi- 

 cient to determine the physiological nature of the tissue. The 

 outer layer, which Prof. Mitscherlich calls the cuticula, is appa- 

 rently the wall of the original cell ; the new cell-walls do not form 

 part of it, being deposited on its interior in successive layers, with 

 which the new septa are continuous. 



With regard to the process of division many modifications of 

 opinion exist ; almost all recent observers however agree in attri- 

 buting the principal influence to the substance which Prof. Mit- 

 scherlich calls the gelatinous mass. This is the Schleim of most 

 German authors, translated by many English authors as mucus, and 

 by myself always as mucilage or mucilaginous matter ; a bad term, 

 and one which it would be desirable to replace universally by the 

 one proposed by H. von Mohl, Protoplasm, which involves no 

 theory of its chemical nature, but certainly is correct in the view 

 it assumes of the function of this matter. Some German authors 

 apply the general term of Inhalt or cell-contents to it : it is the 

 cytoblastema of Schleiden and the endochrome of other authors. 



KutzingJ holds that this protoplasm is enveloped in a special 

 membrane, which he calls the amylid-zelle. H. von Mohl§ de- 



* Ueber das Wacbsthum der Zellmembran. Bot. Zeitung, vol. iv. p.o'57, 

 1846. — Translated in Annals of Nat. Hist. Ser. 1. vol. xviii. p. 145, 1846. 

 Untersuchung der Frage : Bildet die Cellulose die Grundlage sammtlieher 

 vegetabilischen Membran ? Bot. Zeitung, vol. v. pp. 497, 521, 545, 1847. 



t Die Intercellularsnbstanz und ibr Verbaltniss zur Zellmembran bei 

 Pflanzen. Botaniscbe Zeitung, vol. v. p. 289, 1847. 



X Linnaea, 1841, p. 546. 



§ Beitrage zur Entwickelungsgeschichte der Pflanzen. Botaniscbe Zeit- 

 ung, vol. i. IS l.'j. — Translated in Taylor's Scientific Memoirs, vol. iv. p. 91. 



