310 Histology of the Callus Tissue in Althaea rosea. 
formerly characterised by the presence of a very large number of 
pectic outgrowths. After the fusion of the rows, they are 
characterised by a thick cuticular outer membrane, and therefore 
form a resistant edge to the callus-tissue. 
In Althcea , therefore, we have additional evidence supporting 
Mangin’s hypothesis as to the mode of origin of cutin. The two 
essential processes are (i.) the accumulation of the pectic bodies in 
the outer layers of the wall; (ii.) the transformation of the pectic 
bodies on exposure, (a) into pectic mucilages with increase of volume, 
( b ) into cutin, a “ hardening ” process involving the expulsion of 
calcium. 
I wish to acknowledge the kindness and help 1 have received 
from Professor J. B. Farmer, F.R.S., in connexion with the present 
research, which was done during my tenure of a London County 
Council Research Scholarship at the Imperial College of Science. 
LITERATURE. 
Mangin. Journal de Botanique, 1891, 1892, 1893. 
Schiitt. Jahrb. f. wiss. Bot., Bd. 33, 1900, p. 594. 
Jost. Bot. Ztg., Bd. 45, 1887, p. 601. 
Mellinck. Bot. Ztg., Bd. 44, 1886, p. 745. 
Noack. Ber. d. deutsch. Bot. Ges., Bd. 10, 1892, p. 645. 
Schenk. Ber. d. deutsch. Bot. Ges., Bd. 3, 1885, No. 7. 
Luerssen. Bot. Ztg., 1873, p. 641. 
