NEW DISTRIBUTION OF THE VEGETABLE KINGDOM. 227 



sporules, or reproductive bodies, analogous to those which Aero- 

 gens have instead of seeds. The old class of Endogens re- 

 quired therefore to be replaced by 3. Endogens proper, whose 

 organs of propagation are seeds, and 4. Sporogens, commonly 

 called Rhizanths, whose reproductive bodies are spores. 



4. Among Acrogens also two modes of growth occur, so 

 essentially different from each other that they evidently repre- 

 sent different kinds of vegetation. In some of them there is 

 a distinct axis of growth, or stem and root, symmetrically 

 clothed with leaves ; in others they are irregular cellular ex- 

 pansions, destitute of true leaves ; in the former we find a 

 trace of something equivalent to the sexes of Exogens and 

 Endogens, in the latter all indications of the kind disappear. 

 Thus are formed two groups, which may be called 5. Cormogens, 

 where there is a stem and leaves, and 6. Thallogens, where 

 there is no separation of those parts. 



5. To what extent dismemberments of the three classes of 

 Jussieu may be further carried, there is no evidence to show : 

 it is not, however, probable that they are capable of much 

 further increase ; for, with a few exceptions, the affinities of 

 the six primary groups now indicated are too continuous and 

 complete to allow us to suppose that any great physiological 

 or fundamental differences of organization exist among them. 

 Some exceptions, however, do exist. 



6. Among Angiospermous Exogens the Natural orders 

 AristolocMacea, Nepenthacea, Lardizabalacea, Menispermacea, 

 Piperaceae, and some others allied to the latter, stand isolated, 

 as it were, in whatever part of the group they are stationed, 

 having no obvious affinity with any other orders; for we can 

 only regard the approximation of Menispermaceae to Anonacea, 

 &c. as the result of altogether artificial considerations. Now 

 these orders appear to agree in one remarkable circumstance. 

 Instead of their wood being formed by zone deposited over 

 zone, season after season, as is the case in the great mass of 

 Exogens, they never have more than one zone of woody mat- 

 ter, to whatever age they may have arrived. Whether their 

 wood itself is formed exactly in the same way as that of other 

 Exogens, namely, by a gradual external addition of stratum 

 upon stratum, is doubtful ; it is probable that they have a 

 mode of growth of their own, analogous to that of Aristolo- 



