707 



Lest a question be asltecl, " What fixes the relative position of 

 Articulata, Molluscata and Radiata ? " it may be as well to observe 

 that this cannot be altered ; place Molluscata or Radiata at the top, and 

 the relative position of the four groups, will still be exactly as shown 

 above. 



It is now necessary to show a correspondence between this formula 

 of arrangement and that which obtains in the Vegetable Kingdom : 

 the four primary groups of vegetables are placed in a corresponding 

 position below. 



ENDOGENS. 



EXOGENS. 



THALLOGENS. ACROGENS. 



This formula, it will doubtless be observed, is only hypothetical at 

 present, but a little further investigation will remove this impression, 

 and show that it is real. And here it is necessary to go back to the 

 three diminutive groups which have already been noticed as having 

 been lately proposed by Professor Lindley: these are Dictyogens, Gym- 

 nogens, and Rhizogens, all of which I am willing to take as they are, 

 viz.y certain plants which like bats, anteaters and whales, present struc- 

 tural peculiarities which render it difficult to class them with either of 

 the larger groups. It is quite foreign to my purpose to claim for 

 them the title of Classes, Alliances or Orders ; it is sufficient that a 

 botanist of Mr. Lindley's eminence has considered it necessary to 

 separate them from the rest. 



Dictyogens, as will be seen by turning to the paper (Phytol ii. 561) 

 to which I have before alluded, are separated from endogens, because 

 the leaves are "net-veined and deciduous, " and because the roothas its 

 wood arranged " in a solid concentric circle." Still the plants of this 

 gi'oup are monocotyledonous, and are said to have the " wood of their 

 stems arranged in a confused manner with the youngest in the centre." 

 As far as I am aware, these conditions are accepted by all botanists, 

 although Mr. Lindley is the only one who has thought them sufficiently 

 important for the foundation of a new division. Well then, it follows 

 that these plants combine the essential characters of exogens with 

 some of the more obvious and usually distinctive characters of endo- 

 gens, so that we must either consider them a separate class, as Mr. 

 Lindley has done, or endogenoid exogens, or exogenoid endogens. 



