Physiological Studies in Plant Anatomy 255 
out a cylinder of the “ Magnum bonum ” potato, 1-5 cm. in diameter, 
and placed this in moist air until the exposed cut surface of the 
cylinder was covered with periderm. He then cut the cylinder across 
transversely and joined the cut ends together under the protection 
of a rubber band. He found that the cylinder would grow together 
again without the activity of a meristem, provided that one of the 
cut surfaces included at least one tracheid from a vascular strand. 
These experiments show that if suberisation does not occur 
meristem formation may not follow. On the other hand a meristem 
may form without any previous suberisation of the cut surface. Thus 
Appel's observation on the surface of tubers dried in the sun showed 
that very little suberisation occurred here, but such rapidly dried 
potatoes usually show a slight meristem formation beneath the hard 
dry surface although it is somewhat irregular. A simple experiment 
which may easily be performed will also show meristem formation 
without any suberisation. If the cut surface is immediately covered 
with melted paraffin wax and left a few days, examination will show 
regular meristem formation without a trace of previous suberisation. 
These cases of meristem formation are significant. In every case the 
essential antecedent to meristem formation is the blocking of the cut 
surface. When the surface is kept moist and suberisation prevented 
as in the experiments of Olufsen and Kabus described above, then 
the cut surface is not blocked and meristem formation does not 
occur. It will be found also that if the cut surfaces are left under 
boiled water for a week or two, suberisation will not occur and 
meristem formation does not follow. This experiment and the com¬ 
parison with the behaviour of cut surfaces under paraffin wax have 
been proved sufficiently reliable to use as class experiments. 
Meristem formation in these experiments with potato tubers may 
thus be attributed to the blocking of the cut surface. This blocking 
then appears to react upon the tissues within, through the accumu¬ 
lation in the walls and intercellular spaces of a sap which provokes 
the activity of a meristem. In this connection attention may be 
drawn to the following further facts. Appel in his experiments 
shows that in the cut potatoes the vascular bundles show a different 
staining reaction with ammoniacal gentian violet to considerable 
depths below the cut, a reaction connected by him with the presence 
of secreted substances in the vascular strand. As a result of the cut, 
moist air has entered the tissue and probably caused increased 
turgor followed by rapid excretion. The cells at the base of the bud 
probably contribute readily to the secretion, hence Kabus finds that 
