58 Bioiting — TJic Structure of the Cork Tissues in 



In the cork region of Acceiia rcptans very minute inter- 

 cellular spaces are present ; the elongated quadrangular cells 

 are arranged in multiseriate layers of large and small cells, 

 the former situated toward the exterior margin, the latter 

 toward the centre of the section. The roots studied were 

 young, and had only two multiseriate layers, each contain- 

 ing four rows of cells. The annular arrangement is also 

 noticeable from the fact that the inner multiseriate layer is 

 composed of cells whose walls are devoid of pigment, while 

 the outer layer is composed of cells whose walls contain 

 pigment. 



Group RiibecE. — In Riibus occidcntalis and R. villos2is very 

 minute rectangular intercellular spaces are present, but they 

 are not arranged with the regularity that is characteristic of 

 the genera of the foregoing groups. Pigment is present in 

 the contents of the outer sloughing-off layers, although in the 

 sections which I studied the flattened uniseriate layers with 

 pigment were not found. When stained with anihne green 

 these layers appeared to be differentiated, the contents of a 

 uniseriate layer being stained more deeply than those of the 

 multiseriate layers. 



Group RosecE. — In the only species of rose examined, the 

 cork was composed of flattened quadrangular cells ; the whole 

 region consisting of alternating layers of cells with and with- 

 out pigment contents. The interior and exterior tangential 

 walls of the non-pigmented layers are curved outwards, so 

 that the pigmented layers have their cells compressed. The 

 intercellular spaces are minute and are arranged irregularly as 

 in the Group RubccE. 



Group Prunece. — In Prunus inrginiana the cork cells are 

 flattened and tabular in shape. They are uninterruptedly 

 connected with each other, so that there is no trace of inter- 

 cellular spaces. The layers of cells are all uniform in appear- 

 ance, and thus division into annular rings, which has formed 

 so conspicuous a feature of the preceding types, is not observed. 



