NOVESIBER 2, 1896.J 



KNOWLEDGE, 



?57 



is a remarkable feature of our time. In d we have a curve 

 showing how the arable land has diminished since 187tJ. 

 This curve goes down steadily from about eighteen to 

 sixteen million acres. The reduction of wheat-growing 

 alone accounts for most of the loss. Let us extend the 

 curve. By the middle of next century we get to about 

 one-half of the initial acreage. But, of course, " much 

 may happen before then." In curve rf^ is represented 

 the growth of ''permanent pasture.' Some care is 

 required in its interpretation ; but we need not here stop 

 to explain. 



We have made rapid strides of late in national education, 

 and the number of those persons who take up the respon- 

 sibilities of matrimony without being able to write their 

 own names is now small and dwindling. Here we have a 

 pretty straight curve (•/), showing the annual numbers of 

 men in one thousand marriages in England who. signed 

 the register by mark (from 1855 to 1894) ; from two 

 hundred and eighty-eight it descends to forty-sis. Extend- 

 iug, we come to zero about the beginning of next century. 

 From this and other signs we seem to be getting within 

 sight of universal education (or what may be called so) : 

 that millennium in which (by prospectus) we were all to 

 have become virtuous and happy I 



Ireland is, of course, behind us in the matter of education. 

 The curve ;' indicates the percentage of persons five years 

 old and upwards who could neither read nor write in the 

 census years 1851, 1861, etc. Its general course conducts 

 us to zero about 1915, when, it may be hoped, illiteracy 

 should be approximately extinct. 



These signs of progress are, no doubt, gratifying, so far. 

 But there is '• another side to the shield." Let us look at 

 the death rate of suicide in England. The figures are here 

 (<') smoothed with averages of ten. Note the rapid rise. 

 In 1860 the rate was sixty per million persons Uving ; in 

 1894 it was ninety-one I 



Following the general course of the smoothed curve as 

 extended, we come to a rate of one hundred about 1910. 

 Is it not a startling comment on our civilization that so 

 many persons (about fifty-two a week in England, and nine 

 a week in London at present) elect to have done wich it 

 by putting out the light of their earthly life ! 



SOME CURIOUS FACTS IN PLANT 

 DISTRIBUTION.-V. 



By W. BoTTiN.; Hemsley, F.R.S. 



I WILL conclude my remarks on insular floras with a 

 brief account of the flora of the British Islands, 

 which will, perhaps, be more easily followed by the 

 majority of readers, because popular names can be 

 introduced more freely. Persons who have visited 

 adjacent parts of the Continent will have noticed nothing 

 strikingly difl'erent in the vegetation in localities where it 

 is least ati'ected by cultivation ; that is to say, where it has 

 been least disturbed by man. The aspect of the vegetation 

 may be very different in some districts, consequent on the 

 extensive planting of certain kinds of trees — the Lombardy 

 poplar in the North of France, for example ; but the wild 

 flowers and the weeds of cultivation are much the same, 

 according to soil, situation, and elevation. This indicates 

 a recent connection, geologically, with the Continent, and 

 convincing evidence is not wanting to establish the fact. 



The British flora is only a fragment of a flora whose 

 elements have a very wide range ; wider, indeed, than any 

 other. A large proportion of the species extend across 

 Northern Asia to the Pacific, and many are spread all 



round the northern hemisphere. This applies more 

 especially to those inhabiting the colder parts of tbe 

 kingdom, but by no means exclusively, as I shall presently 

 show. A few recur in the mountains of tropical Asia, 

 Africa, and America, and some, as I have already pointed 

 out, reach the southern limits of vegetation. Coming to 

 the genera, a very large number of them are of worldwide 

 distribution. For example, the buttercup genus [Hanun- 

 ciilux), the willow-herb genus {EjiHohium), the speedwell 

 genus (\'eronif(i), and the sundew genus (Drosera), belong 

 to this category ; and each is represented in New 

 Zealand by a much larger number of species than it is in 

 our own country. But before giving further examples of 

 distribution I will give a few comparative statistics bearing 

 on the composition and extent of the British flora. 

 Excluding the so-called critical species — that is to say, 

 species founded on very slight differential characters — of 

 such genera as Riitnis (brambles i, Bosn, and Hieracium 

 (hawkweeds), the number of species of flowering plants 

 and ferns native of the British Islands is less than 

 fifteen hundred, belonging to about five hundred and forty 

 genera and ninety-seven natural orders. The number of 

 natural orders, or families, as they are sometimes termed, 

 in the whole world is about two hundred and ten, so that 

 nearly half of them are represented in this very small 

 area. The total number of genera and species in the 

 whole world is not so easily calculated : but approximately 

 the former amount to between eight thousand and ten 

 thousand, and the latter to between one hundred thousand 

 and one hundred and twenty thousand.' The differences 

 between the highest and lowest of each of these respective 

 totals in a way represents the diversity of opinion among 

 botanists as to the degree to which subdivision should be 

 carried. Further, I may explain, this diversity of opinion 

 is due to the fact that vegetable organisms, as well as 

 animal, are not mathematically definable quantities, but 

 a series or chain of beings, ranging from microscopic 

 one- celled individuals to the most complex and highly 

 organized members of the whole system. Some of the 

 orders, genera, and species of this system are so distinct 

 from their nearest allies as to be easily defined, suggesting 

 the extinction of connecting links ; whilst in other parts 

 of the system the gradations are so slight and the relation- 

 ships so complex that their classification is necessarily, to 

 a greater or less extent, artificial and arbitrary. 



I have already alluded to the cosmopolitan character 

 of the genera of British plants and the wide range of 

 many of the species, and I will now give some further 

 illustrations of these facts. In the first place there is not 

 a single genus peculiar to the islands, nor even one well- 

 defined species ; I mean an easily recognized species such 

 as the daisy or dandelion, and like them easily distinguished 

 from their nearest allies in the native flora. .\ score or 

 two of critical species have been founded on British 

 specimens, and they have not been actually identified with 

 Continental forms : but it does not follow that they do 

 not exist on the Continent. 



Before going further I ought to explain that my remarks 

 refer to the natural distribution of plants as distinguished 

 from colonization consequent on their introduction through 

 human agency. A person going from England to the 

 United States or Canada would see numbers of our corn- 

 field and roadside weeds, apparently as much at home 

 there as here ; but there is good evidence that they were 

 introduced accidentally or intentionally by man, though 



* It should be borne in mind that these numben do not include 

 till" i'\rredingly niuuorous mosses, seawoeds, funguses, and other low 

 oi'ganisuis. 



