1-16 represent zooids seen more or less nearly in profile; figures 17-20 zooids seen from above. Figures 5, 6, 8, 14, 15 were drawn by Mr. Goode; the remainder by the writer. The drawings testify to the entire agreement between the two

observers. The zooids seen by us appear to have been of the mouthless kind. Moseley has noticed the fact that these expand much more readily than the others. Our observations were made partly with a two-inch, but chiefly with a one-inch objective.

Some attempts were made to study the zooids by means of decalcified specimens, previously treated with picric acid and alcohol; a preliminary treatment with picric acid and subsequent removal to alcohol having been shown by experiments

16.

17.

18.

19.

20.

undertaken by members of the United States Fish Commission, in 1874, to be remarkably effective in preserving the delicate tissues of Hydrozoa. We did not succeed in obtaining by this means any zooids in satisfactory condition. The specimens, however, prepared as above stated, and subsequently mounted in glycerine jelly, show well some details of structure, particularly the lasso-cells with extraordinarily long thread, figured by Moseley.* Moseley's figure of a lasso-cell from Millepora nodosa illustrates well the character of those in Millepora alci. cornis, though in the latter the spinous portion is somewhat nearer the base of the thread. The length of the thread in the longest of our specimens is about 027 inch.

*Philosophical Transactions, clxvii, pl. II, fig. 1.

ART. XVII. - Forest Geography and Archaeology; a Lecture delivered before the Harvard University Natural History Society, April 18, 1878; by Asa GRAY.

[Continued from p. 94.]

THE difference in the composition of the Atlantic and Pacific forests is not less marked than that of the climate and geographical configuration to which the two are respectively adapted.

With some very notable exceptions, the forests of the whole northern hemisphere in the temperate zone (those that we are concerned with) are mainly made up of the same or similar kinds. Not of the same species; for rarely do identical trees occur in any two or more widely separated regions. But all round the world in our zone, the woods contain Pines and Firs and Larches, Cypresses and Junipers, Oaks and Birches, Willows and Poplars, Maples and Ashes and the like. Yet with all these family likenesses throughout, each region has some peculiar features, some trees by which the country may at once be distinguished.

Beginning by a comparison of our Pacific with our Atlantic forest, I need not take the time to enumerate the trees of the latter, as we all may be supposed to know them, and many of the genera will have to be mentioned in drawing the contrast to which I invite your attention. In this you will be impressed most of all, I think, with the fact that the greater part of our familiar trees are "conspicuous by their absence" from the Pacific forest.

For example, it has no Magnolias, no Tulip-tree, no Papaw, no Linden or Basswood, and is very poor in Maples; no Locust-trees-neither Flowering Locust nor Honey Locust-nor any Leguminous tree; no Cherry large enough for a timbertree, like our wild Black Cherry; no Gum-trees (Nyssa nor Liquidambar), nor Sorrel-tree, nor Kalmia; no Persimmon, or Bumelia; not a Holly; only one Ash that may be called a timber-tree; no Catalpa, or Sassafras; not a single Elm, nor Hackberry; not a Mulberry, nor Planer-tree, nor Maclura; not a Hickory, nor a Beech, nor a true Chestnut, nor a Hornbeam; barely one Birch tree, and that only far north, where the differences are less striking. But as to Coniferous trees, the only missing type is our Bald Cypress, the so-called Cypress of our southern swamps, and that deficiency is made up by other things. But as to ordinary trees, if you ask what takes the place in Oregon and California of all these missing kinds, which are familiar on our side of the continent, I must answer, nothing, or nearly nothing. There is the Madroña (Arbutus) instead of our Kalmia (both really trees in some places); and

there is the California Laurel instead of our southern Red Bay tree. Nor in any of the genera common to the two does the Pacific forest equal the Atlantic in species. It has not half as many Maples, nor Ashes, nor Poplars, nor Walnuts, nor Birches, and those it has are of smaller size and inferior quality; it has not half as many Oaks; and these and the Ashes are of so inferior economical value, that (as we are told) a passable wagon-wheel cannot be made of California wood, nor a really good one in Oregon.

This poverty of the western forest in species and types may be exhibited graphically, in a way which cannot fail to strike the eye more impressively than when we say that, whereas the Atlantic forest is composed of 66 genera and 155 species, the Pacific forest has only 31 genera and 78 species. In the appended diagrams, the short side of the rectangle is proportional to the number of genera, the long side to the number of species.

Now the geographical areas of the two forests are not very different. From the Gulf of Mexico to the Gulf of St. Lawrence about twenty degrees of latitude intervene. From the southern end of California to the perinsula of Alaska there are twentyeight degrees, and the forest on the coast runs some degrees north of this; the length may therefore make up for the comparative narrowness of the Pacific forest region. How can so meagre a forest make so imposing a show? Surely not by the greater number and size of its individuals, so far as deciduous (or more correctly non-coniferous) trees are concerned; for on the whole they are inferior to their eastern brethren in size if not in number of individuals. The reason is, that a larger proportion of the genera and species are coniferous trees; and these, being evergreen (except the Larches), of aspiring port and eminently gregarious habit, usually dominate where they occur. While the east has almost three times as many genera and four times as many species of non-coniferous trees as the west, it has slightly fewer genera and almost one-half fewer species of coniferous trees than the west. That is, the Atlantic coniferous forest is represented by 11 genera and 25 species; the Pacific by 12 genera and 44 species. This relative preponderance may also be expressed by the diagrams, in which the smaller enclosed rectangles, drawn on the same scale, represent the coniferous portions of these forests.

*We take in only timber trees, or such as attain in the most favorable localities to a size which gives them a clear title to the arboreous rank. The subtropical southern extremity and Keys of Florida are excluded. So also are one or two trees of the Arizonian region which may touch the evanescent southern borders of the Californian forest. In counting the Coniferous genera, Pinus, Larix, Picea, Abies and Tsuga are admitted to this rank, but Cupressus and Chamaecyparis are taken as one genus.

Indeed, the Pacific forest is made up of conifers, with nonconiferous trees as occasional undergrowth or as scattered individuals, and conspicuous only in valleys or in the sparse treegrowth of plains, on which the oaks at most reproduce the features of the "oak openings" here and there bordering the Mississippi prairie region. Perhaps the most striking contrast between the west and the east, along the latitude usually traversed, is that between the spiry evergreens which the traveler leaves when he quits California, and the familiar woods of various-hued round-headed trees which give him the feeling of home when he reaches the Mississippi. The Atlantic forest is particularly rich in these, and is not meagre in coniferous trees. All the glory of the Pacific forest is in its coniferous trees: its desperate poverty in other trees appears in the annexed diagram.

These diagrams are made more instructive, and the relative richness of the forests round the world in our latitude is most simply exhibited, by adding two or three similar ones. Two will serve, one for Europe, the other for N. E. Asia. A third would be the Himalay-Altaian region, geographically intermediate between the other two as the Arizona-Rocky Mountain district is between our eastern and western. Both are here left out of view, partly for the same, partly for special reasons pertaining to each, which I must not stop to explain. These four marked specimens will simply and clearly exhibit the general facts.

Keeping as nearly as possible to the same scale, we may count the indigenous forest trees of all Europe at 33 genera and 85 species. And those of the Japan-Manchurian region, of very much smaller geographical area, at 66 genera and 168 species. I here include in it only Japan, Eastern Manchuria, and the adjacent borders of China. The known species of trees must be rather roughly determined; but the numbers here given are not exaggerated, and are much more likely to be sensibly increased by further knowledge than are those of any of the other regions. Properly to estimate the surpassing richness of this Japan-Manchurian forest, the comparative smallness of geographical area must come in as an important consideration.

To complete the view, let it be noted that the division of these forests into coniferous and non-coniferous is, for the

Japan-Manchurian non-coniferous, 47 genera, 123 species.

In other words, a narrow region in Eastern Asia contains twice as many genera and about twice as many species of indigenous trees as are possessed by all Europe; and as to coniferous trees, the former has more genera than the latter has species, and over twice and a half as many species.

The only question about the relation of these four forest regions, as to their component species, which we can here pause to answer, is to what extent they contain trees of identical species. If we took the shrubs, there would be a small number, if the herbs a very considerable number, of species common to the two New World and to the two Old World areas respectively, at least to their northern portions, even after excluding arctic-alpine plants. The same may be said, in its degree, of the North European flora compared with the Atlantic North American, of the Northeast Asiatic compared with the northern part of the Pacific North American, and also in a peculiar way (which I have formerly pointed out and shall have soon to mention) of the Northeastern Asiatic flora in its relations to the Atlantic North American. But as to the forest trees there is very little community of species. Yet this is not absolutely wanting. The Red Cedar (Juniperus Virginiana) among coniferous trees, and Populus tremuloides among the deciduous, extend across the American continent specifically unchanged, though hardly developed as forest trees on the Pacific side.