72 Tr A ^'^S ACTIONS OF THE AMERICAN INSTITUTE. 



of the primeval flora to goologic time. The oldest rocks we know, 

 the Eozoic, have afforded no plants, so far as we know, at all. The 

 nc'it series, the Paleozoic, include the oldest land plants we know. 

 But in the Mesozoic period we arrive at a different flora, and in the 

 Cainozoic, or modern period, we have other floras. It is the Paleo- 

 zoic flora only of which I shall speak to-night. During the whole of 

 the paleozoic period, the seaweeds have existed. In the earlier per- 

 iods the classes of Acrogens and Gymnosperms far exceeded the Exo- 

 gens and Endogens, while the reverse is the fact at the present day. 

 The warm and moist climate of portions of the southern hemisphere 

 at the present day now have a flora more nearly resembling the 

 early epochs than any other portions of the earth. The Uniformity 

 of the flora of that early period indicates a temperature nearly 

 uniform throughout the earth. At present we have in our atmos- 

 phere but a small quantity of carbonic acid gas. If we had more, it 

 would tend to make the climate more uniform, by preventing the 

 radiation of heat from the earth. The carbon locked up in our coal 

 mines, and then existing in the atmosphere, may therefore have been 

 at least one reason for the uniformity of climate on the earth in the 

 paleozoic period, the flora of that day indicating a warm and moist 

 cliinate. 



Taking the Flora of the carboniferous period as typical of that, of 

 the paleozoic in general, we find that there was a vast amount of 

 vegetation, afterward made fossil and becoming coal. In that moist, 

 warm, but unwholesome atmosphere, we find the Sigillaria or seal- 

 tree, one of those most abundant in the swamps of the carboniferous 

 period. Here we have a large, tall stalk, without branches, or per- 

 haps divided into a few branches, covered with long leaves. "We have 

 remains showing the ribbed structure of the stalk, and the sears of 

 the leaves. There are no trees in our latitude resembling it in struc- 

 ture. We know of the fruit of the Sigillaria only by the abundance 

 of certain nuts, the Trigoriocarpa, that are found around them. Trees 

 of two and three feet in diameter were not uncommon. The root of 

 this tree is more remarkable even than its stem, having attracted the 

 attention of geologists before the stem, and obtained the name of 

 Stigmaria. These roots are bifurcated and sprea^ out in a remarkably 

 regular way, all the little rootlets spreading as regularly as leaves. 

 These roots occur very often in the coal formation without the stems, 

 and at first it was supposed that they were the whole of the plant. 

 The first process in the formation of a bed of coal, was usually the 



