<:. ELEMEM'A 



VI. Sieve Tissue. 



Illustration-. Stem of Cucurbitaceae (Cucumber or Pumpkin). 



PREPARATION: This material should be hardened in alcohol 

 and treated as directed on p. 21. Both longitudinal and transverse 

 sections are to be cut, stained with haematoxylin, aHd several of 

 each permanently mounted. In the longisection, portions must be 

 secured that contain some of the fibro-vascular tissue. In the lat- 

 ter section on the outer and inner edge of the bundle, 



OBSERVE : 1. The thin walled sieve tubes, recognized by 

 their sieve like plates, forming septa at the ends, and not infre- 

 quently on the lateral walls. 



2. The protoplasmic contents of the tubes, frequently denser 

 near the ends. 



3. The structure of the sieve plates. 



4. The sieve pores, of varying sizes, usually largest at the 

 center. 



5. A clear glistening bluish mass surrounding the sieve 

 plate, the callus plate. 



6. A mass of slime collected at the end of the tube, with a 

 portion of it projecting through the pores of the sieve. To a mount 

 of fresh tissue add qulphuric acid, and observe its effects on the 

 plates. 



In the transectinir. 



OBSERVE : 1. The fibro vacnlar bundles arranged regularly 

 around the peripheral portion of the -ton. 



2. Two nearly circular or crescent shaped masses of tissue, 

 (stained with haeniiitoxyliu a dark purple) one on the axial and one 

 on the peripheral side of the bundle, The Phloem. 



3. By careful focusing upon some of the larger of the open- 

 ings in these areas, sieve plates, forming septa. 



Goodale, p. 92; Vines' Text Book of Bot., p. 136; DeBary, p. 

 172 ; Strasburger, p. 121 ; Annales des Sciences Naturelles, (Bot.) 

 Vol. X., pp. 193-324 ; Prings. Jahrb., 21, 253-292. 



7. Laticiferous Tissue. 



1. Latex cells. 



2. Latex vessels. 



Illustration : For simple LATEX CELLS. 



