107 MEEISTEM TISSUE. 



the center, and consisting of thick-walled scalariform vessels and 

 xylem parenchyma. 



4. Outside of the xylem and completely surrounding it, a 

 band of tissue limited by the bundle sheath, The Phloem. This 

 part of the bundle consists of cribose tissue, and phloem paren- 

 chyma. 



Make a longitudinal section of the bundle and identify in it, 

 all of the tissues seen in the transectiou. 



It is to be noted that in this bundle the xylem portion is com- 

 pletely enveloped by Phloem and both surrounded by the bit //<//>' 

 sheath. The opposite arrangement of Phloem and Xylem is not 

 infrequently found. 



Illustration Second : CONCENTRIC BUNDLE in the Rhizome of 

 IRIS. (Fig. 23.) 



PREPARATION : Trausections may be cut free-hand or treated 

 as previously directed for herbaceous stems. By carefully focus- 

 ing on one of the smaller bundles, 



OBSERVE : 1. In the center, the thin- walled cells of the 

 Phloem with a few sieve plates here and there in the larger open- 

 ings. 



2. The large thick-walled cells outside of the Phloem and 

 surrounding it, the Xylem. 



Vines' Text Book of Bot., p. 175 ; Strasburger, p. 145 ; De- 

 Bary; p. 339 ; Bessey, p. 107 ; Sedgwick and Wilson's Biology, 

 pp. 72, 78. 



