90
ILLUSTRATIONS OF INDIAN BOTANY-
which at their origin are generally equal in number to the divisions of the corolla, in- stead of being placed opposite to these divisions, and passing through their axes as in other plants, alternate with them ; each of the vessels at the top of the tube dividing into two equal branches, running parallel to and near the margins of the corresponding lacinest, within whose apices they unite. These, as they exist in the whole class, and are in a great part of it the only vessels observable, may be called primary. In several genera, however, other vessels occur, alternating with the primary, and occupying the axes of the lacineas ; in some cases these secondary vessels being most distinctly visible in the lacinea-, and becoming gradually fainter as they descend the tube, might be regarded as recur- rent ; originating from the united apices of the primary branches ; but in other cases, where they are equally distinct at the base of the tube, this supposition cannot be ad- mitted. A monopetalous corolla, not splitting at the base, is necessarily connected with this structure, which seems also peculiarly well adapted to the dense inflorescence of Composita? ; the vessels of the corolla and stamina being united and so disposed as to be least liable to suffer by pressure."
Geographical Distribution. Representatives of this family are found in all parts of the world from the polar circles to the equator, and, according to DeCandolle, its species amount to nearly one-tenth of the Vegetable Kingdom. But, though thus gen- erally distributed and, as a whole, form so large a proportion of the vegetation which covers the globe's surface, they are far from being equally prevalent, in proportion to the indigenous vegetation in different countries. According to Humboldt, every 7th flowering plant of France is a Composita; in Germany, every 8th; in Lapland, every loth; in North America, every 6th ; in tropical America, every 3d ; of the North of New Hol- land, according to Brown, every 16th; and of a small collection formed on the banks of the Congo in Africa, every 23d. In Sicily, every 3d, the same in the Balearic Islands, while in Melville Island the proportion is nearly the same as in the tropical parts of New Holland, or about In India, taking Wallich's List as the standard, they occur in the
proportion of These examples, which may be viewed as approximations to the truth,
serve to show, with sufficient precision, the inequality of their distribution as well as the want of any fixed ratio of increase and decrease corresponding with latitude. On this subject, however, it is well remarked by Lindley, much still remains to be learned, and as I am myself only acquainted with the small fragment of the order appertaining to the Indian Peninsula, I am not in a position to throw light on its obscurities. I may however remark, that the number of alpine species of our flora is greater in proportion to the rest of the vegetation than on the plains. The number found above 3000 feet of elevation amounting to probably about 150 species, which I imagine is nearly in the ratio of 1 in 15 or 16 of the flowering plants of these regions.
DeCandolle gives the following summary as the result of his examination of the natural habit of Compositse. "Out of 8523, of which he had any knowledge, 1229 were annuals, 243 biennials, 2491 perennials, 2264 under shrubs from 1 to 3 feet high, 366 shrubs from 4 to 15 feet high, 72 small trees, 4 large trees above 25 feet high, 81 woody plants of which nothing further was known [I have seen the Neilgherry Mo?iosis, ranked in this division, fully 40 or 50 feet high, R. W.], 126 twiners or climbers, and 1201 about which nothing certain could be ascertained. These were distributed as follows : — 347 in the South Sea Islands, 2224 in Africa, 1827 in Asia, 1042 in Europe, and 3590 in America. Of these the Cape of Good Hope possessed 1540, Mexico 725, Brazil 722, United States and Canada 678, the Levant 610, the Continent of India 681, North and Middle Europe 447, Europe at the Mediterranean 595, Australia 294." Lindley, extract- ed from D. C.'s Collection of Memoirs, No. X.
The following note, from M. Laseque's Musee Botanique de Delessert, regarding the proportion this family bears to the rest of the vegetable kingdom, is interesting. After stating that the order at the present day includes more species than was known altogether to Linnaeus, he adds in a note: "It is a singular fact, that the proportion Composita? bear to the whole of the known vegetable kingdom, has always been about the same,
