1884.] of the cell-wall and middle-lamella. 99 



Wigand 1 showed, mucilage may also be produced by the dis- 

 organisation of starch-grains and, as Trecul 2 and Prillieux 3 found, 

 even from the protoplasm itself, we must not carry this assumption 

 too far. It was an interesting observation made by Prillieux that 

 in the gum-producing cells of the cherry-tree, the substance in 

 question first appeared between the middle lamella and the last 

 layer of cell- wall, thus resembling the similar phenomenon which 

 occurs in connection with the appearance of oil, &c. beneath the 

 cuticle in glandular hairs and the like as described by Personne 4 

 in the hop, by Cohn 5 in Siphocampylus, by Batalin 6 in Sarracenia, 

 and more recently in the extended observations of Martinet 7 , 

 Bonnier 8 and Behrens 9 . 



Gums and mucilages occur in all parts of the plant. In many 

 of the Leguminoseae, the gum, e.g. gum-tragaganth, is produced 

 by the disorganisation of the cell-walls of the pith and medullary- 

 rays 10 , and in the Rosaceae, e.g. the cherry, it is formed both in 

 the cortex, the medullary rays, and even from certain of the 

 parenchyma-cells of the vascular tissue 11 . The mucilage of seeds 

 is usually derived from the middle layers of the thickened 

 epidermal cells, but it also occurs in cells containing raphides ; in 

 definite passages as in the Marattias 12 , from rows of cells as in the 

 Marchantias 13 ; or according to the interesting observation of de 

 Bary 14 is secreted by certain hairs at the base of the petiole of 

 Osmunda. The mucilaginous degeneration undergone by the 

 outer layers of the walls of so many algae has long been known, 

 but has recently been prominently brought into notice in con- 

 sequence of the observations of Schmitz 15 upon the surface growth 

 of cells. It is also a matter of some interest that in the parenchyma 

 cells of many ordinary vegetable tissues the same phenomenon 



1 Wigand, Ueber die Desorganisation der Pflanzenzelle, &c. Pring's Jahrb. in. 

 115, 1863. 



2 Trecul, Prods Verbal des Seances de la Societe philomatique pendant Vannee, 

 1862. 



3 Prillieux, Ann. des Sci. Nat. ser. 6, I. 1875. 



4 Personne, Ann. des Sci. Nat. ser. 4, i. 1842. 



5 Colin, De cuticula, Wratislaviae, 1850. 



6 Batalin, Ueber die Function der Epidermis von Sarracenia, &e. St Petersburg, 

 1880. 



7 Martinet, Ann. des Sci. Nat. ser. 5, xrv. 1871. 



8 Bonnier, Ann. des Sci. Nat. ser. 6, vm. 1879. 



9 Bebrens, Flora, 1878, 1879. 



10 Von Mobl, Bot. Zeit. 1857. 



11 Prillieux, loc. cit. 



12 Harting et de Vriese, Monogr. des Maratt. 



13 Prescber, Die Scbleimorgane der Marchantieen. Sitzber. d. h. Akad. in 

 Wien, lxxxvi. 1882. 



14 De Bary, Vergl. Anatomie, p. 105. First mentioned by Milde, Monogr. 

 Generis Osmundae. 



15 Scbmitz, Sitzber. niederrhein. Ges. in Bonn, Dee. 6th, 1880. See also 

 Sitzber. Versammlung deutscher Naturf. u. Aerzte in Eisenach, Sept. 19th, 1882. 



7—2 



