708 



One of these courses we must adopt, and I am content with either, 

 for either will fix their station between the typical endogens and 

 the typical exogens, and will show that these great classes lead into 

 each other. 



The class Gymnogens, in prior works by the same author, is made 

 to combine the pines, the equiseturas and some other groups, but in 

 the present publication the equisetums are omitted, and carried over 

 the boundary which has hitherto separated them from acrogens, a 

 group in which they are generally included by other authors. The 

 plants in this class are separated from the other exogens by the cha- 

 racter, " seeds quite naked." The facial or superficial approach of 

 the pines to the extinct Calamites, of these again to equisetums and 

 tree-ferns, is obvious to all ; much might also be said of the pecu- 

 liar wood of the Coniferaj, which has lately attracted so much atten- 

 tion, and has shown how this group recedes from the true exogenous 

 structure, and approaches the acrogenous structure of the ferns, without 

 displaying, as far as I can detect, a similar approach to the structure 

 of the endogens, so that by means of the gymnogens, whether we con- 

 sider them a distinct class or not, we must pass from the exogens to the 

 acrogens without the intervention of the commonly interposed class of 

 endogens. 



"At this point of the Vegetable Kingdom," says Mr. Lindley, 

 " there is a plain transition from the highest form of organization to 

 the lowest. Gymnogens are essentially exogens in all that apper- 

 tains to their organs of vegetation ; they have concentric zones in their 

 wood, a vascular system, in which spiral vessels are found, and a 

 central pith ; but they are analogous to reptiles in the Animal King- 

 dom, inasmuch as their ova are fertilized by direct contact with the 

 male principle. The two most remarkable of the orders are conifers 

 and cycads. Of these, the former is connected with club-mosses 

 among acrogens by means of the extinct genus, Lepidodendron, and 

 their branches are sometimes so similar to those of certain lycopods 



* " Among endogens no difference has been remarked in the mode of propagation, but 

 a material peculiarity has been noticed in the manner of growth. In the great mass 

 of the class the stem and root are formed in a similar way, or there is no considerable 

 difference between them, and the leaves have no articulation with the stem ; but in a 

 part of them the root is exactly like that of an exogen without concentric circles, and 

 the leaves fall off the stem by a clean fracture, just as in that class. Such fundamen- 

 tal distinctions have given rise to the separation by me of endogens into — 1. Endo- 

 gens proper, and 2. Dictyogens." — Lindley^ Veg. Kingd. 4. 



The above is correctly quoted, but the statement that the root is " without concen- 

 tric circles '' of woody matter is evidently a misprint. G. L. 



