Phloem Stele Structure & Vascular Bundles

Lab No.7 Phloem Stele structure & Vascular bundles Slides Prepared 1- Cucurbita stem c.s 2- Zea stem c.s & L.S 3- Tilia stem c.s 4- Pinus old stem c.s. 5- Cucurbita pumkin l.s Demonstration 1- Ranunculus root c.s 2- Helianthus stem c.s Fresh Specimen - Ecbalium stem 1 Lab No.7 Phloem Stele structure & Vascular bundles 1- Phloem The food conducting tissue in seed plants. Associated with xylem in vascular system. Complex tissue composed of - Sieve elements (sieve tubes / sieve cells) - Companion cells / albuminous cells - Parenchyma - fibers It is of two types: - primary phloem which originates from procambium. - Secondary phloem which originates from vascular cambium. - 1)Phloem in angiosperms A) Herbaceous dicots (Primary phloem) Primary phloem: - appears in bundles with primary phloem - in a form of protophloem and metaphloem which are distinguishable - protophloem which mature before the plant elongates, consists of sieve tube elements , companion cells may not be present, this protophloem will be crushed later by stretching. - metaphloem which matures after the plant completes its elongation or during elongation. Consists sieve tube elements, companion cells, parenchyma, no fibers. Exercise 1 study a prepared slide for Cucurbita stem c.s and another slide for Cucurbita stem L.s -Primary phloem is seen as bundles on both sides of primary xylem (bicollateral vascular bundles) -notice the protophloem and metaphloem - Components of primary phloem are sieve tube elements (living protoplast but lack nucleus) (with sieve areas at end walls on sieve plates where protoplast of two superimposed sieve tube elements are interconnected). Callose carbohydrate 2 other than cellulose forms the basic framework of sieve plate (you may be able to notice), companion cells (small cells), parenchyma which is intermediate in size between sieve tube elements and companion cells. In the L.S. notice the sieve tubes, sieve plates and you may be able to notice the companion cells. B) Herbaceous monocots (primary phloem) Exercise 2 study a prepared slide for Zea stem c.s & l.s -Notice components of primary phloem (sieve tube elements, companion cells and parenchyma) in c.s then observe it in l.s C) Woody dicots (Secondary phloem) Exercise 3: study a prepared slide of Tilia stem c.s Secondary phloem appears in a form of two types of wedges -wedges containing sieve tube elements, companion cells, axial parenchyma and fibers -wedges of parenchyma (dilated ray parenchyma) 2)Phloem of gymnosperms Exercise 4: study a prepared slide for Pinus stem c.s -Phloem of pinus is primitive -functioning phloem next to cambium -nonfunctioning crushed phloem outward toward the cortex. -notice that phloem in Pinus as a gymnosperm is made of sieve cells (rectangular empty cells(devoid of contents)) with weak specialized sieve areas on lateral walls (no sieve plates), axial parenchyma that some of them differentiate into albuminous cells, other parenchyma cells with darkly stained tannin near the nonfunctioning phloem, ray parenchyma (uniseriate), fibers are absent in pinus (may be present in other gymnosperms) - resin ducts may be present in secondary phloem Exercise 5 - prepare a hand cross section of Ecbalium stem -Try a hand longitudinal section also for Ecbalium stem - use Toluidine blue. - locate xylem and phloem in c.s - try to identify components of phloem tissue in L.S. 3 2- Stele Structure -Stele (column) is the core of the plant axis (stem and root) including (primary vascular system and all interfascicular regions, gaps, pith (if present) and pericycle. - based on the distribution of vascular and non-vascular tissues in primary state of development stele could be 1] Protostele (no pith) A) Haplostete B) Actinostele (Ranunculus root cs. & Psilotum aerial stem c.s) C) Plectostele (Lycopodium root c.s) 2] Siphonostele (pith present, continous xylem & phloem) A) Siphonostele amphiphloic B) Siphonostele ectophloic (Tilia stem c.s) 3] Dictyostele (siphonostele dissected by leaf gaps) 4] Eustele (Cucurbita stem c.s & Helianthus stem c.s) primary vascular tissues in strands separated by parenchyma tissue or leaf gap 5] Atactostele (Zea stem c.s) Exercise 6 examine the prepared slides mentioned previously and determine type of stele in each. Name of slide Type of stele Sketch for this type Ranunculus root cs. Psilotum aerial stem c.s Lycopodium root c.s 4 Cucurbita stem c.s Helianthus stem c.s Zea stem c.s 3) Vascular Bundles Depending on arrangement of xylem and phloem within the bundle there are several types of vascular bundles. Exercise 7: Examine the prepared slides mentioned beside each type of the vascular bundle , try to recognize the type of the vascular bundle mentioned and draw a sketch for it. A) Collateral vascular bundle (Helianthus young stem c.s & Zea stem c.s) B) Bicollateral vascular bundle (Cucurbita stem c.s) C) Concentric vascular bundle 1) Amphicribral (Pteridium rhizome c.s.) 2) Amphivasal X P 5 6 Lab 8 The root Slides: Prepared 1) Allium root tip L.S. 2) Ranunculus root C.s 3) Vicia root C.S. 4) Tilia root C.S. 5) Pinus root C.S. 6) Smilax root C.S 7) Orchid root C.S 8) Lupinus root C.S nodules nitrogen fixing Fresh Specimens 1) Germinated seed (bean) 2) Carrot 3) Monocot root (fibrous root) 4) Dicot root (tap root) 5) Legume root with nodules 1