48 CLASSIFICATION OF PLANTS. [chap. 



The vegetable kingdom may be divided into 

 flowering and flowerless plants ; while flowering plants 

 again fall into two divisions, known as Dicotyle- 

 dons or Exogens and Monocotyledons or Endogens. 

 Dicotyledonous or exogenous plants are those in 

 which, when the seed germinates, the "plumule" or 

 bud arises between two (rarely more) seed-leaves or 

 cotyledons of the embryo, or from a terminal notch. 

 In this class the leaves have their nerves branched, 

 forming a sort of network, as in the oak, beech, 

 clover, violet, &c. In their growth they increase by 

 forming new woody tissue over the old, whence the 

 term " Exogenous." In a Dicotyledonous or exo- 

 genous tree, therefore, we find a number of con- 

 centric circles, each representing a period of growth, 

 and indicating, though roughly, its age in years. 

 Monocotyledonous or endogenous plants, on the con- 

 trary, are those in which the plumule or bud is de- 

 veloped from a sheath-like cavity on one side of the 

 cotyledon. The leaves have parallel nerves, as for 

 instance in grasses, orchids, lilies, palms, &c. In a 

 cross-section the wood shows no concentric circles, 

 but consists of bundles of woody fibre irregularly 

 imbedded in cellular tissue. Both these classes have 

 flowers. 



Cryptogams, on the contrary (ferns, mosses, sea- 

 weeds, lichens, fungi, &c.), have no flowers, and 

 multiply by bodies called spores. 



That the colour of the corolla has reference to the 

 visits of insects is also well shown by the case of those 

 flowers, which — as, for instance, the ray or outside 

 florets of Centaurea — have neither stamens nor pistils. 



