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Winifred Blackwell. 
been called mucilaginous (Noack), protoplasmic, circularised 
(Luerssen, Mellinck), or related to cutin (Jost), and finally Mangin 
has shewn convincingly that in intercellular spaces the papillae 
most often consist of calcium pectate. 
Fig. 1. Callus in Althaa rosea. I. Wound callus tissue arising from pith. 
II. Wall of callus cell showing papillae (stained with iodine). III. Papillae 
very highly magnified. Lettering:— a, meristematic zone with much starch ; 
b, normal pith cells; c, thickened walls of collapsed pith cells at wound 
surface ; d, hypertrophied callus cells with papillate walls ; e, papillae ; /, 
central spot stained blue with iodine. 
It was thought worth while to investigate, micro-chemically, 
the papillae on the callus walls of Althcea, to see if the nature of 
their substance could be determined, and hence, to find an explanation 
for the discrepancies in accounts of those who have formerly 
observed them. Micro-chemical investigations were made difficult 
by the exceedingly small size of the papillae, but by repeating each 
test several times, and by examining under a objective in doubtful 
cases, some results were obtained which may be regarded as 
accurate. 
The reactions given in Althcea differ from any as yet reported. 
Some of these differences may be correlated with the fact that the 
material examined had been preserved for a considerable time in 
alcohol; the varying results obtained by different authors make it 
more probable that the substance of the papillae is really variable. 
So far two main views have been held as to the nature of the 
