FERN STEM. 



95 



Bl-COLLATERAL BUNDLES. 



Make cross-sections of the hardened stem of Pumpkin, Squash 

 or Watermelon. 



The bundles consist of a xylem mass betwen an outer and an 

 inner phloem mass. In the xylem are some very large ducts, 

 looking like large holes, with some smaller ones in the inner 

 portion. There is a large quantity of small-celled parenchyma 

 tissue. The phloem masses consist of large sieve cells and 

 accompanying parenchyma cells. There are no bast fibres 

 present nor any wood fibres in the xylem. There are two layers 

 of cambium cells, one between the xylem and outer phloem 

 mass, the other between the xylem and inner phloem mass. The 

 rest of the section is made up of very large-celled parenchyma 

 tissue. 



CONCENTRIC BUNDLES. 



I. Variety with phloem surrounding xylem. 



Make cross-sections of the rhizome of the Eagle Fern (Pteris 

 aquilina) and stain with phloroglucin. 



On the exterior is the epidermis, brown in color, then several 

 layers of thick-walled fibrous cells, also brown, known as the 

 hypoderma. Interior to this is a zone of large ordinary par- 

 enchyma cells with starch grains. Then comes a circle of bun- 

 dles, separated from one another by parenchyma. The bundles 

 may be round or elongated, but never radially. Within this 

 circle of bundles are two elongated masses of thick-walled, 

 fibrous cells, dark colored. Lying between these are two bun- 

 dles, elongated and larger than those of the circle. The spaces 

 between the objects just described are filled up with paren- 

 chyma cells. 



In the center of the bundles is the xylem, composed of large 

 scalariform ducts stained red and a few small parenchyma cells. 

 Surrounding the xylem 

 is the phloem, unstain- 

 ed, consisting of a layer 

 of small parenchyma 

 cells with fine starch 

 grains immediately next 

 to the xylem; then a 

 layer of sieve cells and 

 their companion cells, 

 finally another layer of 

 small starch - bearing 

 parenchyma cells. The 

 bundle is sharply divid- 

 ed off from the sur- 

 rounding parenchyma Fig 5 8 ._Sllghtly magnified section of stem of 



by a well-developed ring 

 of elongated prismatic 

 cells, known as the en- 

 dodermis or bundle sheath. 



C le ; d. one of the two bundles In the center ; e, 

 brown mass of fibrous cells (Baatln). 



