1. OBJECTIVES : 1. Learn the basic anatomy of plant dermal tissue. 2. Develop knowledge of the associated terminology. 3. Appreciate the diversity of types of epidermis tissues on plant species. 4. View epidermal structures. 5. Make leaf surface impressions for viewing surface features and to identify epidermal features. 6. Review terminology and structures introduced in week one of the lab. OVERVIEW: In this lab you will learn about dermal tissue. This tissue, also known as the plant epidermis, forms the outermost layer of cells and is usually only one cell layer thick. Epidermal cells typically are flattened and rectangular in shape. Epidermal cells can have various functions depending on the type of plant and where they are in the plant body.

6. Plants and animals both have a layer of tissue called the epidermal layer . Plants have special pores called stomata to allow passage of material. The stomata pores are surrounded on both sides by jellybean shaped cells called guard cells. Unlike other plant epidermal cells, the guard cells contain chlorophyll to do photosynthesis. This allows the cells to expand/ contract to open or close the stomata. Guard cells also close when dehydrated. This keeps water in the plant from escaping. The opening or closing of guard cells can be viewed in a microscope by adding different water concentration to the leaf tissue. Most stomata are on the lower epidermis of the leaves on plants (bottom of the leaf). The number of stomata on the epidermal surface can tell you a lot about a plant. Usually, a high concentration of stomata indicates fast growth and wet climate. Lower concentrations of stomata indicate lower rates of photosynthesis and growth or adaptations for dry weather Purpose: To view and compare the stomata from the leaves of several species of plant STUDY OF STOMA Introduction

9. Fossils tell the story About four hundred and fifty million years ago, at the end of the Ordovician and in the beginning of the Silurian, the land was desolate and empty. Barren, hardly wethered rockgrounds, empty sand-, gravel- and clayplains, no green. Maybe some lichens. And at wet spots some algae with a couple of spider-like little creatures creeping around. In the neighbourhood of the mouth of rivers, where the water regularly flooded the land, it was probably green with algae. At such places, e.g. in Australia, traces of big seascorpions have been found. There was not much happening on the land. Life enacted itself nearly completely in the water. The oldest indications for the existence of real land plants have been found in cores from boreholes in Oman. They contained fours of mutually connected spores (tetrads) enveloped by remains of the spore sac in which they had been formed. Research on the spore walls point to a relationship with the liverworts. The fossils have been found in the Middle Ordovician and are about 475 million years old . How plants conquered the land

10. Cooksonia The first fossils of macroscopic land plants have been found in the Middle Silurian of Ireland. They are about 425 million years old. They consist of small bifurcations some centimeters in size. Only in the very last part of the Silurian fossils of land-plants become more common and also more complete. The best known plant from that time is called Cooksonia . It is named after Isabel Cookson, who occupied herself with intensive collecting and describing plantfossils. The little plant looked very simple: a stem which bifurcated a couple of times topped with small spheres in which the spores were formed. Thus sporangia. No leaves, no flowers, no seeds. And roots? Probably horizontal growing stems, connected with the soil by root hairs, took the function of roots. But this is not sure for fossils proving this have not been found yet. During many millions of years it was mainly this kind of plants that grew on humid places on the land. The evolution from algae to land plants must have been a lengthy process. Many conditions had to be fulfilled before plants were able to maintain themselves on the land. There is at first the everlasting danger of desiccation .

11. The remedy which developed is a thin waxy layer at the surface of the plant: the cuticle. Generally algae don't have a cuticle, nearly all land plants do. But a land plant also has to breath and it needs the possibility to assimilate carbondioxide from the air to generate its nutriments. Thus the isolation by the cuticle can not be absolute. That's why the stomata have evolved, which can be opened and closed if necessary.Another problem for land plants is that they miss the upward force of the water. To be able to keep upright supporting tissue is needed. Already in Cooksonia xylem vessels have been recorded. These are vessels with annular or spiral shaped thickenings at the walls, which give them solidity. Through these vessels water is transported from the soil to the plant cells. Another important adaptation to landlife is the very tough wall that evolved around the spores. This provided the spores with an excellent protection against desiccation, fungi, and so on. In fact they became nearly invulnerable, for they have been fossilised very often. Species of Cooksonia are found at several places on earth, e.g. in Wales, Scotland, England, Czechia and Canada. The finding of a fairly complete plant is a rare occurrence. I was already very glad with the bifurcated little stem with two sporangia between Cooksonia -chaff on the photo. Cooksonia has become extinct in the Early Devonian.

12. The vascular cambium is a lateral meristem in the vascular tissue of plants. The vascular cambium is the source of both the secondary xylem (inwards, towards the pith) and the secondary phloem (outwards), and is located between these tissues in the stem and root. A few leaf types also have a vascular cambium. [2] The vascular cambium usually consists of two types of cells: Fusiform initials (tall cells, axially oriented) Ray initials (almost isodiametric cells - smaller and round to angular in shape) The vascular cambium is a type of meristem - tissue consisting of embryonic (incompletely differentiated) cells from which other (more differentiated) plant tissues originate. Primary meristems are the apical meristems on root tips and shoot tips. Another lateral meristem is the cork cambium , which produces cork, part of the bark. Vascular cambia are found in dicots and gymnosperms but not monocots , which usually lack secondary growth. For successful grafting , the vascular cambia of the stock and scion must be aligned so they can grow together. Structure of Vascular Cambium

13. The function of the vascular cambium is to produce secondary growth, thus the vascular cambium must be formed before secondary growth can occur Function Of Vascular Cambium

14. 1. Root-stem transition was investigated in Solanum tuberosum, Lycopersicum esculentum, Datura tatula, Physalis virginiana, Petunia acuminata, and Solanum pseudo-capsicum. 2. The method of transition in each of the plants investigated is the same and agrees with the method in Solanum melongena. 3. Illustrations of transition of the potato were used as representative of the other members of the group. The first change from the diarch, radial protostele of the root is a breaking up of the xylem plate and a division of each of the two primary phloem groups into three distinct parts. 4. This is followed by a bifurcation of the metaxylem of the two primary xylem units. These units were not observed to swing outward, one following a left and the other a right curve, as reported by Artschwager. 5. The central groups of phloem cells from each side differentiate toward the center of the axis and become the internal phloem. Each of the four remaining groups is gradually inclined in a tangential direction toward the original position of the protoxylem points. This development continues until the bicollateral condition is established. ROOT STEM TRANSITION

15. 6. One of the primary xylem units, formed by the breaking of the original diarch xylem plate and consisting of one protoxylem point, its metaxylem, and internal and outer phloem groups, becomes the vascular trace of one cotyledon; the second unit, that of the other. 7. In the cotyledonary petiole and midrib the protoxylem differentiates adaxially and finally is nearer to the upper epidermis than is the metaxylem. Simultaneously the metaxylem differentiates abaxially until the endarch condition is established