88 Mr W. Gardiner, On the constitution [Feb. 11, 



In the substance of the walls themselves also, changes both 

 of a chemical and physical nature supervene, in consequence of 

 which, the typically cellulose membrane becomes lignified, cuti- 

 cularised, corky or mucilaginous as the case may be. 



As we follow the history of the development of botanical 

 histology and microchemistry, we find that in each of the above- 

 mentioned kinds of cell-walls, certain substances were discovered, 

 to the properties of which, the peculiar characteristics of the wall 

 were due. Thus from the cuticle first described by Brogniart 1 , 

 Fremy 2 isolated a substance, to which he appropriated the name 

 Cutin, and for which he gave the percentage composition, C. 73'66, 

 H. 11'37, O. 14"97. In the same way lignified walls are usually 

 allowed to owe their properties to the presence of lignin 3 . In 

 corky walls, Chevreul 4 found a substance, which he called Suberin, 

 which according to Doepping 5 gave eerie acid (impure suberic acid) 

 after treatment with nitric acid, and was expelled from a corky 

 tissue in yellow drops on treatment with boiling potash 6 . As to 

 mucilaginous walls, the presence in them of mucilage or gum 

 was long known. Kiitzing 7 (by boiling) isolated from the cells of 

 certain algae, e.g. Sphaerococcus crispus, a mucilage to which he 

 gave the name Phytogelin, and also recognized that gum-traga- 

 ganth consisted of a mass of swollen cell-walls, the cells of which 

 often contained starch grains 8 . More recently also Frdmy 9 described 

 as pectose, a body allied to mucilage which is found in many 

 unripe fruits and Berg 10 in investigating Getraria islandica separated 

 from it Lichen-starch and Lichenin. 



At a very early period 11 it was recognized that in cells which 

 had become lignified, cuticularised, mucilaginous or corky, an 

 unaltered cellulose portion still remained, and the foreign matters 

 (lignin, cutin, &c.) which prevented the visible occurrence of the 

 cellulose reactions, were regarded as infiltrated substances. Thus 

 Von Mohl found that in the case of epidermal and corky cells, 

 a lengthy treatment with potash, dissolved out the foreign matter, 

 and the remaining cell- wall now gave a blue coloured with iodine. 



1 Brogniart, Ann. de Sci. Nat. Ser. i. t. xxi. p. 427 (1830). 



2 Fremy, Ann. de Sci. Nat. Ser. iv. t. xii. (1859). 



3 Payen, Mem. sur les dSveloppements des vegetaux (1844). 



4 Chevreul, Sur le moyen a, analyser plusieurs matieres ve'ge'tales, &c. Ann. 

 de Chemie, t. 96 (1815). 



5 Doepping, Ann. Ghem. u. Pharm. von Liebeg u. Wohler, Bd. 45, p. 286 (1843). 



6 Von Hohnel, Ueber Kork, &e. Sitzber. d. k. Akad. in Wien, lxxvi. (1877). 



7 Kiitzing, Phycologia generalis. 



8 Kiitzing, Grund. d. phil. Bot. 203, 204. 



9 Fremy, Ann. de Sci. Nat. Ser. 6, t. xin. (1882). 



10 jjerg^ Zur Kenntniss des in Cetraria islandica &c. Diss. Dorpat, 1872. 



11 Scharcht, The Microscope, English translation, p. 69. Von Mohl, Vegetable 

 Cell, English translation, p. 28. 



