STEMS. 



21 



The following table shows at a glance the distinguishing 

 characteristics of the three great classes of the vegetable 

 kingdom : — 



Exogenous or dicoty- 

 ledons 



Endogenous or mono- 

 cotyledons 



Acrogenous or 

 acotyledons 



Flowering plants 

 (phanerogams) 



Flowering plants 

 (phanerogams) 



No true flowers 

 (cryptogams) 



Two or more cotyle- 

 dons 



One cotyledon 



No cotyledons 



Wood in rings 



Wood in isolated 

 bundles 



Wood in patterns 

 (not rings) 



Net-veined leaves 



Parallel-veined leaves 





As mentioned in a previous lesson, the stem — as well as 

 other parts of the plant — presents distinguishing character- 

 istics by which monocotyledonous and dicotyledonous 

 j)lants can be readily distinguished. It is in relation to the 

 stem that the words exogen (outer growth) and endogen 

 (inner growth) are applied, as will now be explained. 



Exogens or Dicotyledons. 

 {Producing two seed-leaves in early growth.} 

 The plants belonging to this class form a large majority 

 of the vegetable kingdom. All the native trees of Great 

 Britain are exogens; while our Australian bottle-trees, 

 gums, wattles, Pittosporums, sheoaks, native tea-trees, and 

 many others, are exogens. The stem of an exogen, in its 

 early period of growth, is a cylinder of cellular tissue. This 



