INTRODUCTION. 



L SKETCH OF THE ELEMENTS OF BOTANY. 



!• Vegetable Tissue. 



1. Plants are primai'ily composed of minute membranous vesicles or cells, 

 which are endowed with the power of reproduction, and through which, al- 

 though closed and destitute of visible pores or openings, the juices of the plant 

 are readily transmitted. 



2. Variously modified, these cells form the Elementary Tissues ; viz. Cellular 

 Tissue or Parenchyma, Woody Tissue or Woody Fibre, and Vascular Tissue or 

 Vessels and Ducts. 



3. Cellular Tissue, which exists in all plants, and of which those of the lower 

 orders are wholly composed, consists of cells aggregated together, and cohering 

 by their contiguous surfaces. 



4. Woody Tissue is composed of slender and elongated cells, with firm and 

 thickish walls, collected in threads or bundles. 



5. Vascular Tissue is made up of larger cells, either in the form of continuous 

 tubes, or forming such by the union of their extremities. In some of these, the 

 walls are marked with dots, lines, or bands ; while in others they are lined with 

 spirally coiled fibres which are capable of being unrolled. The latter are called 

 Spiral Vessels, and exist only in plants which bear proper flowers. 



6. Of these tissues are formed the Organs of plants ; viz- Organs of Vegetation, 

 consisting of the Root, Stem, and Leaves, and Organs of Reproduction, consisting 

 of the Flower and Fruit. 



3. The Root. 



7. The Root, or Descending Axis, is that part of the plant which grows down- 

 ward, commonly penetrating the soil, from the moisture of which it imbibes 

 nourishment. It branches indefinitely and without order, but bears no other 

 appendages. Its ultimate branches are called Rootlets. 



8. Roots which descend immediately from the embryo are termed Primary 

 Roots. They are called Tap-Roots, when they consist of one thick and fleshy 

 piece ; fascicled or clustered, when of several fleshy branches springing from a 

 common centre; tuberous when the branches become greatly enlarged and filled 

 with starchy matter ; and fbrous, when all the parts are slender and thread-like. 



