52 PKACTICAL BOTANY. 



from it by an irregular line, is a parenchymatous tissue, 

 consisting of cells which appear nearly square in the 

 transverse section ; each cell has plentiful protoplasm, 

 a nucleus, and several chlorophyll corpuscles : the walls 

 are more or less thickened, swollen, and stratified : here 

 and there are to be seen pits closed by a thin, highly- 

 refractive pit-membrane. These two tissues (1) and (2) 

 together constitute the cortical band above recognised 

 under a low power. 



Here, as in other cases of pitted tissues, the question of per- 

 foration of the pit-membrane has been raised : though the actual 

 proof is in this case difficult, it is asserted by various authors that 

 the continuity of protoplasm through the pit-membrane has been 

 actually observed. 



3. The above tissue graduates off without definite 

 limit into the medulla, of which the chief character- 

 istic is the excessive bulk of the swollen cell-walls : an 

 idea of the manner in which this comes about may be 

 formed by following the gradual transition from cortex 

 to medulla, when it will be apparent that the parts of 

 the wall adjoining the middle lamella (and sometimes 

 the middle lamella itself) swell greatly to form a 

 gelatinous matrix, in which the cells appear to be 

 embedded, each being surrounded by a definite, firm, 

 cellulose wall. Here and there "trabecular" filaments 

 will be found running in the plane of section. If 

 sections be stained with Schulze's solution the firmer 

 cell-wall stains pale blue, but the swollen matrix does 

 not stain. 



Occasionally a section may be found which has 

 passed through one or more of the sterile or neutral 



