60 Bunting—The Structure of the Cork Tissues in 
rece and Rubee the results of all the above tests indicate 
that the youngest uniseriate layer is composed of cells which 
early show suberized radial walls, and feebly, if at all, suber- 
ized tangential walls. In the older uniseriate layers, both 
radial and tangential walls are suberized, although there 
usually is a delicate cellulose lamella within the suberized 
wall. The youngest multiseriate layer is made up of cells 
whose walls are mainly formed of cellulose. These may or 
may not have a delicate lamella of suberin surrounding the 
cellulose; this suberin lamella usually increases in amount in 
the older layers of the section. In some cases, however, cellu- 
lose may be present in cell walls even after several annual 
rings have been formed. Thus cellulose has been noted in 
Alchemilla pyrenaica in the fifth multiseriate layer; while both 
in this species and in others the multiseriate layers may show 
suberization at a much earlier period. In the species of rose 
studied, the cell walls of the entire cork region are made up 
of suberin as well as cellulose lamellae, while in the species 
studied of the groups Pruxee and Pomee the cell walls are 
strongly suberized. If the cell walls are pigmented the color 
must be extracted, before characteristic cork tests with alcan- 
nin and chlorophyl extract are obtained. 
In the application of all of these tests, an oak stem was used 
as a control, so that there might be reasonable certainty that 
the chemicals employed were such as would give the charac- 
teristic reaction with a substance known to be cork. All the 
tests employed gave excellent results with the oak stem, but 
with the very delicately suberized groups of Rosacee the most 
satisfactory reactions were obtained by iodine and sulphuric 
acid. The use of chlorophyl extract, alcannin, osmic acid, 
etc., was far from satisfactory in these groups, although in 
Prunce and Pomee they proved excellent tests for the differ- 
entiation of the cork. The question naturally presents itself 
as to whether these tests are less delicate than iodine and 
or whether there is a different 
, 
sulphuric acid or ‘Schultze,’ 
