THE 
HEW PHYTOIiOGIST. 
Vol. XII, Nos. 9 & 10. Nov. & Dec., 1913. 
[Published December 31st, 1913.] 
THE HISTOLOGY OF THE CALLUS TISSUE IN 
ALTHAEA ROSEA. 
By Winifred Blackwell, 
Imperial College of Science and Technology. 
[With One Figure in the Text.] 
T is well known that typical wound callus tissue is formed by the 
renewed growth of certain living cells in the neighbourhood of 
the wound, in a direction perpendicular to the surface of the wound. 
Subsequently, repeated tangential walls are laid down, so that 
elongated cell rows are formed, which later fuse, probably by the 
softening and partial hydrolysis of their walls, to form a pseudo- 
parenchymatous tissue, in which further differentiation may or may 
not occur, although the outer edge of the tissue becomes constantly 
suberised. 
In the course of an investigation on wound reactions in the 
pith of Althcea rosea , a stage in callus formation was found, in which, 
owing to the weakness of the wound stimulus, cells here and there 
had grown to form rows, without lateral fusion. Careful exami¬ 
nation revealed the fact that the outer surface of the wall of these 
cells was not smooth but was studded with minute outgrowths in 
the form of short rods or stalked spherical heads (Fig. 1), obviously 
of secondary formation and of different substance, since they 
remained uncoloured with chlor-zinc-iodine in contradistinction to 
the rest of the wall which became violet. Kuster has described 
this warted condition of the wall as characteristic of young callus 
tissue, and it is also interesting to note that Mangin has found 
analogous structures very frequently on the walls lining the inter¬ 
cellular spaces of plants. They therefore appear to be characteristic 
of the walls of cells not normally exposed. In spite of the frequency 
of the occurrence of these papillae, investigations as to the nature of 
their substance have led to rather conflicting results. They have 
