VEGETABLE ORGANISATION 
426 
vwich many :: these tribes are connected together so intimate, that the 
di ffi culty botanists experience in the arrangement of the objects of 
their studies frequently consists more in the separation of allied plants 
and families, titan in their union with each other into groups. 
“ The structure of the powdery lichen, and of its aided species, is 
most simple consisting of vesicles only, and those scarce!- connected 
together O ther forms of the vast tribe of li chens—these humble indi¬ 
viduals of the vegetable race which form the first of Nature's coverings 
—which act, as it were, the part of pioneers, and, though of small 
repute, and to the unobservant eve insignificant—are the very instru¬ 
ments which it has rleased the Almighty Creator and Ruler of all to 
employ as the secondary agents of his power in breaking down the sur¬ 
face of the hard and barren rock, and rendering many a wild and 
uncultivated region fit for the nourishment o: larger tribes of plants* 
ana ultimatelv afar tec to the higher orders of animals—ms. ear. of man 
himself. Other forms of the vast—and shall we not say important?— 
fami!" of rlants are found in which these primary vesicles are closely 
compacted into musts cf dims, crusts of extreme tenuity, but covering 
the surface of stones, and rocks, and the bark of trees. Such -are the 
curious Lecidecz geqgrap lica, so called from its resemblance to a than 
or map; the Graphis elegans , and Opegrapka scrip fa —a species of 
mimic writing, &c. Fj.e transitions from these filmy expansions to 
the micaceous lichens—such as the common yellow wall-lichen. Far - 
melia parietina , and its allies—by the splitting up, as it were, of the 
crust, in dineren: directions from the surface to which it is attached, 
into scales or lamina of various thickness—as in Squamaria and otheis 
of the scalv lichens—is —ed known ; 2nd again mom these through the 
Cetraria Jslcmdica, or Iceland moss, and others in which these scaly 
and leafv crusts are gradually lengthened into thongs, to the fibrous or 
filamentous lichens on the one hand, and into some of the tribe of Alg&, 
or sea-weeds, on the other. 
The same gradual development of the cellular structure may be 
traced in the —a familv of '"lanes, the greater number of which 
are inhabitants of the ocean. This is observable in their fructification, 
from the simple vesicles of Parpfag/ra and Ulm 1, to tie variously com- 
uounlec granules of Gracdaria. Rkadomeia, and Microcladia —manges 
accompanied by corresponding "anati'ns in the structure and configura¬ 
tion of the entire plants. 
The transition fren the Alg<s to the mosses, in which the external 
firm approaches still more to those vegetable tribes where the cells, 
becoming gradually more elongated, approach more or less to the 
tubular structure, is well marked by some of the Hepatic<s } or liver- 
