6o Btaiting — Tlie Structure of the Cork Tissues in 



rceece and Rubcm the results of all the above tests indicate 

 that the youngest uniseriate laj'cr 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 

 Alclicmilla pyretiaica 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 lamellze, while in the species 

 studied of the groups Pninece and Poincce 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 RosacecB 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 

 PrunecB and Poniccu 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 

 sulphuric acid or "Schultze," or whether there is a different 



