ANATOMICAL STRUCTURE AND VITALITY. 



63 



The second are called vascular plants (from vas, a 

 tube), or Phcenogams, and include all flowering plants, 

 ■which hold the highest rank in the vegetable king- 

 dom, having flowers with stamens, pistil, and perfect 

 seed. 



According to Dr. Lindley's "Vegetable Kingdom," 

 published in 1853, above 92,000 species of plants were 

 said to be known to botanists ; but by new discoveries 

 since then the number may now be calculated at not 

 less than 100,000, of which 15,000 may be set down as 

 cellular or flowerless, and 85,000 as vascular or flower- 

 ing plants. It is the latter we have now to consider, 

 and the mode of classifying them into families ; they 

 present important distinctive characters, dividing them 

 into two great divisions, which are readily distinguish- 

 able from each other in three ways : — First, by the seed ; 

 secondly, by the mode of thickening of the stem ; thirdly, 

 by the leaves. 



The mode of formation and increase in the size of the 

 stem takes place in two distinct ways : — First, by a suc- 

 cessive formation of cellular, vascular, and woody tissue, 

 round a central axis called the pith, and is of two kinds 

 — the inner being the solid or woody part of the tree, 

 the outer, less solid, called the lark. Between the bark 

 and the wood successive annual layers of new structure 

 are deposited in the form of concentric, solid, erect 

 cones, each cone answering to a year's growth, and 

 are well marked in transverse and vertical sections of many 

 trees, especially of the Fir family. From the centre or 

 pith proceed erect, thin plates in the form of rays, which 

 unite with the annular circles of increase, proceeding on 

 to the bark, and are called medullary rays. In a trans- 

 verse section, they appear like spokes passing through a 



