Ciup. II. GENERA. IGl 



by their forms. I would also liirther remark, that there i.s one question relating 

 to the form of animals, Avhich I have not touched here, and which it is still more 

 important to consider in the study of plants, namely, the mode of association of 

 individuals into larger or smaller communities, as we observe them, particularly 

 among Polyps and Acalephs. These aggregations have not, as far as their form 

 is concerned, the same importance as the form of the individual .animals of which 

 they are composed, and therefore seldom afford trustworthy family characters. But 

 this point may be more appropriately considered in connection Avith the special 

 illustration of our Hydroids, to which my next volume is to be devoted. 



I have stated above, that botanists have defined the natural families of plants 

 with greater precision than zoologists those of animals ; I have further remarked 

 also, that most of them make no distinction between orders and families. This 

 may be the result of the peculi;ir character of the vegetjible kingdom, which is 

 not built upon such entirely different plans of structure as are animals of different 

 branches. On the contrary, it is possible to trace among plants a certain gradation 

 between their higher and lower types more distinctly than among animals, even 

 though they do not, any more than animals, constitute a simple series. It seems 

 to me, nevertheless, that if Cr3-ptogams, G^Tnnospenns, Monocotjdedons, and Dico- 

 t^'ledons can be considered as branches of the vegetable kingdom, analogous to 

 Kadiata, Mollusks, Articulata, and ^^crtobrata among animals, such divisions as Fungi. 

 Algoa, Lichens, Mosses, Hepatica?, and Ferns in the widest sense, ma}- be taken as 

 classes. Diatomaceae, Confervas, and Fuci may then be considered as orders ; Mosses 

 and Hepaticae as orders ; Equisetacea>, Ferns proper, Hydropterids, and Lycopodiaceae 

 as orders also ; as they exhibit different degrees of complication of structure, while 

 their natural subdivisions, which are more closely allied in form or habitus, may 

 be considered as families ; natural families among plants having generally as distinct 

 a port, as families among animals have a distinct form. We need only rememljcr 

 the Palms, the Conifene, the Umbellifera:', the Compositas, the Leguminosse, the Lab- 

 iatae, etc., as satisfactory examples of this kind. 



SECTION y. 



GEXERA. 



Linnaeus already knew very well that genera exist in nature, though what he 

 calls genera constitute frequently groups to which we give at present other names, 

 as we consider many of them as families; but it stands proved by his writings 



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