viii CONTENTS 



PAUE 



III. The Primary Meristems 04 



IV. Secondary Meristems - 98 



CHAPTER III. 

 THE DERMAL SYSTEM. 



I. General Considerations ..... . 100 



II. The Epidermis 101 



A. The Simple Epidermis - - - - - - 102 



1. The Shape of Epidermal Cells 102 



2. The Outer Epidermal Wall. Wax - - - - 102 



3. The Radial and Inner Epidermal Walls - - 112 



4. Cell-contents - - - - - - - 114 



5. Subsidiary Functions of the Epidermis - - 119 



B. The Multiple Epidermis 122 



C. Epidermal Appendages - - - - - - - 125 



III. Periderm - - - - - 133 



A. Cork - - 134 



B. The Phellogen 140 



IV. Bark 142 



V. The Dermal System among Thallophyta - - - - 145 



VI. Ontogeny of the Dermal System - - - - - 148 



CHAPTER IV. 

 THE MECHANICAL SYSTEM. 



I. General Considerations 150 



II. Mechanical Cells - - - - - - - - 152 



A. Form and Structure of Mechanical Elements - - - 152 



1. Bast-fibres (Bast-cells) 152 



2. Wood-fibres (Libriform-cells) - - - - - 155 



3. Collenchyma - - - - - - - 155 



4. Sclerenchymatous Cells (Sclereides) - - - - 158 



B. Strength and Elasticity of Mechanical Cells - - 161 



III. Principles Governing the Construction of the Mechani- 



cal System 165 



A. Inflexibility - - - - - - - 165 



B. ^extensibility - - - - - - - - 167 



