REFERENCES 65 



areas of the primary wall. These thickened areas will be seen 

 to be restricted largely to the cell-corners, hence the term "angu- 

 lar" collenchyma. Especially in sections stained with neutral 

 red, the wall thickenings exhibit evidence of a lamellated struc- 

 ture. Observe that "spaces," varying greatly in size and dis- 

 tribution, occur throughout the collenchyma tissue. Some of 

 these apparent "spaces" represent the trans-sectional appear- 

 ance of the narrow tapering ends of collenchyma cells ; others are 

 true intercellular air spaces. The distinction between these two 

 conditions is best appreciated, however, by a study of longi- 

 sections of the tissue. Note the highly vacuolate cytoplasm and 

 the chloroplasts in the collenchyma cells. 



To understand thoroughly the shape of collenchyma cells and 

 the distribution of the thickened areas of their primary walls, 

 examine under low and high magnification longi-sections of the 

 Datura petiole. Study carefully the band-like thickenings of the 

 wall and note their relationship in adjacent cells. The inter- 

 cellular spaces should now be more evident. Simple pits may be 

 seen in both face and section views. Observe that individual 

 cells are often subdivided by thin transverse or sloping walls. 



III. Suggested Drawings and Notes. — 



1. Draw on a large scale a sector of the trans-section of the 

 petiole of Datura (or of the substitute material previously listed) 

 about 5 to 6 cells in width, extending from the epidermis to the 

 cortical parenchyma tissue. Label carefully all important 

 structures. 



2. Prepare a drawing of a small portion of the collenchyma 

 tissue as seen in longi-sectional view. Show clearly the distribu- 

 tion of the thickened areas of the wall, the pitting and the inter- 

 cellular spaces. Fill in the contents of a single collenchyma cell. 



3. Summarize, in the form of laboratory notes, the evidence 

 discussed by Esau (1936) which shows that the walls of collen- 

 chyma cells are rich in water. 



REFERENCES 



1. Anderson, D., Ueber die Struktur der Kollenchymzellwand 

 auf Grund mikrochemischer Untersuehuiigen. Sitzber. 

 Akad. Wiss. Wien. Math.— Natur. Kl. 136 .-429-440. 1927. 



