48 BOTANICAL GAZETTE [JULY 
pectose. This pectose is further transformed into pectic acid and 
pectin. The final stage is the breaking down of the calcium pectate 
of the middle lamella. 
4. Oxidases are present in the epidermal and phloem tissues in 
both stems and petioles. In the abscission layer they are present 
in all tissues outside of the xylem, and increase in amount with the 
age of the abscission layer. 
5. Slight traces of iron may be found in practically all parts 
of stem and petioles, but shortly before abscission there is a sudden 
CIO of iron in the abscission layer. 
. The amount of oxalates remains fairly constant throughout 
the ae life of the leaves. There is no evidence of an increase 
of calcium oxalate crystals in the cells of the abscission layer at the 
time of abscission, nor are there any crystals of calcium oxalate 
in the walls of these cells. 
7. Calcium in solution is abundant in all living cells of the plant 
except those of the abscission layer at the time of abscission, where 
it practically disappears. 
Discussion 
According to ToLLENsS (16), pectose is an oxidized cellulose of 
the composition 9(CsH:0O;)—CcH:.Os. The first step in the 
breaking down of the cell walls in abscission in Coleus is evidently 
one of oxidation of cellulose. This process is possibly a result of 
the accumulation and subsequent activity of oxidases in the 
abscission layer, and also of the catalytic action of iron on these 
oxidases. This may be merely an acceleration of the conversion 
of cellulose into pectose which ordinarily goes on in cell walls of © 
plants with increasing age. Cellulases may play a part in this 
process, but the question is still to be investigated. Ever (4) 
succeeded in isolating a cellulase in a fungus, Merulius lacrimans, 
which was capable of altering cellulose, but cellulases in higher 
plants are still unknown. CzAPEK (2) and EuLER (3) have called 
attention to the fact that our knowledge of cellulases is very limited. 
The pectose formed from the cellulose is in turn readily trans- 
formed to pectic acid and pectin, and in this process the catalytic 
action of iron may again play an important réle. Whether acids 
