The principles of biology . e class of plants to which we now turn—that of Acrogens-7-is nearly related by its lower members to the classes abovedealt with : so much so, that some of the inferior liverwortsare quite licheniform, and are often mistaken for over these, let us recommence our analysis with suchmembers of the class, as repeat those indications of progresstowards a higher composition, which we have just observedamong the more-developed Algce. The Jungermanniacecefurnish us with a series of types, clearly indicating the transi-tion from an aggregate of the second orde
The principles of biology . e class of plants to which we now turn—that of Acrogens-7-is nearly related by its lower members to the classes abovedealt with : so much so, that some of the inferior liverwortsare quite licheniform, and are often mistaken for over these, let us recommence our analysis with suchmembers of the class, as repeat those indications of progresstowards a higher composition, which we have just observedamong the more-developed Algce. The Jungermanniacecefurnish us with a series of types, clearly indicating the transi-tion from an aggregate of the second order to an aggregateof the third order. Figs. 41, and 42, indicate the structureamong the lowest of this group. Here there is but an incom-plete development of the second order of aggregate. The THE MORPHOLOGICAL COMPOSITION OF PLANTS. 25 frond grows as irregularly as tlie thaUus of a Kdien: it is in-definite in size and outline, spreading hither or thither as theconditions favour. Moreover, it lacks the differentiations re-. quired to subordinate its parts to the whole: it is uniformlycellular, having neither mid-rib nor veins; and it puts outrootlets indifferently from aU parts of its under-surface. InFig 43, Jungermannia epiphylla, we have an advance on thistype. There is here, as shown in the transverse section. , a thickening of the frond along its central portion, pro-ducing something Kke an approach towards a mid-rib; andfrom this the rootlets are chiefly given off. The outKne, too,is much less irregular ; whence results greater distinctnessof the individuality. A further step is displayed in Junger-mannia furcata, Fig. 45. The frond of this plant, compara-tively well integrated by the distribution of its substancearound a decided mid-rib, and by its comparatively-definiteoutlines, produces secondary fronds—there is what is calledproliferous growth ; and, occasionally, as shown in Fig. 46,representing an enlarged portion, the growth is doubly-pro-liferous. In thes
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectbiology, bookyear1864
