717 



very simple in the Vegetable Kingdom, because of the similar modes 

 of life observable among plants, while, on the contrary, the act of pro- 

 pagation is highly diversified, on account of the very varied nature or 

 structure of the parts by which it is accomphshed; so might we con- 

 jecture that the organs of nutrition would afford but few distinctions 

 available for purposes of classification, while those of fructification 

 would furnish many. And such is the fact. Hence it is, that the 

 great classes of plants are principally distinguished by their organs 

 of growth, and that in the numerous minor groups such peculiarities 

 are comparatively disregarded, their chief distinctions being derived 

 from their parts of reproduction." — L. V. K. xxvi. 



And again, according to his axioms : — 



" 1. Peculiarities of structure which are connected with the man- 

 ner in which a plant is developed are physiological ; those which are 

 connected with the manner in which parts are arranged are structu- 

 ral. Physiological characters are of two kinds, viz., those which are 

 connected with the mode of growth (the organs of vegetation J , and 

 those which regulate reproduction (the organs of fructification). 

 Physiological characters are of greater importance in regulating the 

 natural classification of plants than structural. 



" 3. The internal or anatomical structure of the axis, and of the 

 foliage, is of more importance than any other character; because 

 these are the circumstances which essentially regulate the functions 

 of growth and the very existence of an individual." — Ih. 



Now, examining the rhizogens by these axioms, we will endeavour 

 to ascertain how far Mr. GriflEith's objections to them as a class are 

 well founded. He declares that " in the construction of the group 

 called Rhizantheae, whatever its rank may be, a remarkable diversity 

 of characters has been sacrificed to an appearance resulting from pa- 

 rasitism on roots, and to an assumed absence of any ordinary form of 

 vegetable embryo." — {Linn. Trans, xix. 303). But these objections 

 surely fall to the ground, when we consider, first, the far more strong- 

 ly marked diversity of character exhibited by plants composing the 

 other classes of the Vegetable Kingdom ; and secondly, the evident 

 affinity existing among the true rhizogens, with regard to their habit 

 and structure. For instance, what can possibly be more unlike, in 

 nearly every character, among endogens, than the towering, highly 

 developed, terrestrial palms, and the minute, simple, aquatic duck- 

 weeds .'' And yet, they are both placed, not only in the same class, 

 but in the same division of that class, notwithstanding that in the one 

 we find the lowest, and in the other the highest degree of structural 

 Vol. II. 4 x 



