ENDOGENS. 101 



slit on one side, in the cavity of which the phimule reposes ; or, finally, the 

 emhryo is a flat plate as in grasses, with the lilumulc and radicle attached 

 to its face near the base. In the latter case the flat plate is a solitary 

 cotyledon, which, in the second instance, is folded together so as to give 

 the emhryo the appearance of being slit, and which in the first, or most 

 habir,ual, condition is not only folded up, but united at its edges into a case 

 entirely burying the plumule and cotyledon. Hence the embryo of an 

 endogen is called monocotyledonous ; a name that is really unexceptionable, 

 notwithstanding the occasional apj)carance of a second rudimentary cotyle- 

 don, as occurs in common wheat. M. Adrien de Jussieu has endeavoured 

 to show that the slit, which is generally supposed to be peculiar to the 

 Arums and their allies, is of general occm-rence in the endogenous embryo. 

 {A?i?i. Sc. N. Ser. xl p. 341.) 



It has already been stated that the radicle is protruded in germination 

 from within the substance of the embryo ; the base of the radicle is con- 

 sequently surrounded by a minute collar formed of the edges of the aperture 

 produced by the radicle upon its egress. For this reason Endogens are called 

 endorhizal. 



Hence the great natural class of plants forming the subject of these 

 remarks has five most important physiological peculiarities, by all which 

 combined, or usually by each of which separately, the class may be 

 characterised. 



1. The wood is endogenous. 



2. The leaves are straight-veined. 



3. The organs of fructification are ternary. 



4. The embryo is monocotyledonous. 



5. The germination is endorhizal. 



It may however be readily supposed that, vicAved as a large class of 

 plants, Endogens are essentially characterised only by the combination of 

 these five peculiarities, and that occasional deviations may occur from every 

 one of them. Thus in Naias, Caulinia, Zannichellia, and others, which con- 

 stitute a part of w^hat Professor Schultz names Homorganous floriferous 

 plants, the whole organisation of the stem is so imperfect that the endo- 

 genous character is lost ; but their true nature is nevertheless suflScieiitly 

 indicated by their straight veins, monocotyledonous embryo, &lc. The 

 examples of a concentrical arrangement of the woody bundles, above 

 alluded to, may be regarded as instances of endogenous development tend- 

 ing towards the exogenous, and are usually looked upon as cases of transi- 

 tion from one form to the other — perhaps not very correctly. Of a similar 

 nature are the resemblances between the columnar Cj'cadaceous Gymuo- 

 sperms and Palms, between the livid, foetid, one-sided calyx of Aristolochia 

 and the equally livid, foetid, one-sided spathe of Araceous Endogens, or, in 

 another point of view, between such lenticular plants as Lemna in Endogens, 

 with the leaves and stems fused, as it were, together, and similar forms of 

 stem and leaf among Marchantiaceous Acrogens. 



Really intermediate forms of vegetation connecting Endogens with other 

 classes, are extremely uncommon. One of the most striking is that which 

 occurs between Ranunculacese and Nymph£eace?e on the part of Exogens, 

 and Alismacese and Hydrocharacese on that of Endogens ; if Ranunculus 

 lingua, or better R. parnassifolius, is contrasted with Alisma plantago, or 

 Damasonium, leaving out of consideration subordinate differences, it will be 

 found that there is little of a positive nature to distinguish them except the 

 albuminous dicotyledonous seeds of the former as compared with the exal- 



