Sept. 13, 1888] 



NATURE 



475 



ing up the scanty data which are available in herbaria and else- 

 where. This has stimulated European residents in China to 

 collect more material, and the fine collections which are now 

 being rapidly poured in upon us will, if they do not overwhelm 

 us by their very magnitude, go a long way in supplying data for a 

 tentative discussion of the relations of the Chinese flora to that 

 of the rest of Asia. I do not doubt that this will in turn explain 

 a good deal that is anomalous in the distribution of plants in 

 India. The work of the Committee has been practically limited 

 to Central and Eastern China. From the west, in Yunnan, the 

 French botanists have received even more surprising collections, 

 and these supplement our own work in the most fortunate 

 manner. I have only to add, for Asia. Bossier's " Flora 

 Orientalis," which practically includes the Mediterranean basin. 

 But I must not omit the invaluable report of Brigade-Surgeon 

 Aitchison on the collections made by him during the Afghan 

 Delimitation Expedition. This has given an important insight 

 into the vegetation of a region which had never previously been 

 adequately examined. Nor must I forget the recent publication 

 of the masterly report by Prof. Bayley Balfour on the plants 

 collected by himself and Schweinfurth in Socotra, an island 

 with which the ancient Egyptians traded, but the singularly anom- 

 alous flora of which was almost wholly unknown up to our time. 



The flora of Africa has been at present but imperfectly worked 

 up, but the materials have been so far discussed as to afford a 

 tolerably correct theory of its relations. The harvest from Mr. 

 Johnston's expedition to Kilimanjaro was not as rich as might 

 have been hoped. Still, it was sufficient to confirm the con- 

 clusions at which Sir Joseph Hooker had arrived, on very slender 

 -data, as to the relations of the high-level vegetation of Africa 

 generally. The flora of Madagascar is perhaps, at the moment, 

 the most interesting problem which Africa presents to the 

 botanist. As the rich collections, for which we are indebted to 

 Mr. Baron and others, are gradually worked out, it can hardly 

 be doubted that it will be necessary to modify in some inspects 

 the views which are generally received as to the relation of the 

 island to the African continent. My colleague, Mr. Baker, 

 communicated to the York meeting of the Association the results 

 which, up to that time, he had arrived at, and these subsequent 

 material has not led him to modify. The flora as a whole presents 

 a large proportion of endemic genera and species, pointing to 

 isolation from a very ancient date. The tropical element is, 

 however, closely allied to that of Tropical Africa and of the 

 Mascarene Islands, and there is a small infusion of Asiatic types 

 which do not extend to Africa. The high-level flora, on the 

 other hand, exhibits an even closer affinity with that temperate 

 flora the ruins of which are scattered over the mountainous 

 regions of Central Africa, and which survives in its greatest 

 •concentration at the Cape. 



The American botanists at Harvard are still systematically 

 carrying on the work of Torrey and Gray in the elaboration of 

 the flora of Northern America. The Russians are, on their 

 part, continually adding to our knowledge of the flora of 

 Northern and Central Asia. The whole flora of the North 

 Temperate Zone can only be regarded substantially as one. 

 The identity diminishes southwards and increases in the case of 

 the Arctic and Alpine regions. A collection of plants brought 

 us from high levels in Corea by Mr. James might, as regards a 

 ■large proportion of the species, have been gathered on one of our 

 own Scotch hills. 



We owe to the munificence of two English men of science the 

 organization of an extensive examination of the flora and fauna 

 of Central America and the publication of the results. The 

 work, when completed, can hardly be less expensive that of the 

 results of the Ckallntgtr voyage, which has severely taxed the 

 liberality of the English Government. The problems which 

 geographical distribution in this region presents will doubtless be 

 found to be of a singularly complicated nature, and it is im- 

 pissible to over-estimate the debt of gratitude which biologists 

 of all countries must owe to Messrs. Godman and Salvin when 

 their arduous undertaking is completed. I am happy to say 

 that the botanical portion, which has been elaborated at Kew, is 

 all but finished. 



In South America, I must content myself with referring to the 

 great "Flora Hrasiliensis," commenced by Martius half a 

 century ago, and still slowly progressing under the editor-hip of 

 Prof. Urban, at Berlin. Little discussion has yet been attempted 

 of the mass of material which is enshrined in the mighty array 

 of volumes already published. But the travels of Mr. Ball in 

 South America have led him to the detection of some verv 



interesting problems. The enormous pluvial denudation of the 

 ancient portions of the continent has led to the gradual blending 

 of the flora of different levels with sufficient slowness to permit 

 of adaptive changes in the process. The tropical flora of 

 Brazil, therefore, presents an admixture of modified temperate 

 types which gives to the whole a peculiar character not met 

 with to the same degree in the tropics of the Old World. On the 

 other hand, the comparatively recent elevation of the southern 

 portion of the continent accounts, in Mr. Ball's eyes, for the 

 singular poverty of its flora, which we may regard indeed as still 

 in progress of development. 



The botany of the Challenger Expedition, which was also 

 elaborated at Kew, brought for the first time into one view all 

 the available facts as to the floras of the older oceanic islands. 

 To this was added a discussion of the origin of the more recent 

 floras of the islands of the Western Pacific, based upon material 

 carefully collected by Prof. Moseley, and supplemented by the 

 notes and specimens accumulated with much judgment by Dr. 

 Guppy. For the first time we were enabled to get some idea 

 how a tropical island was furnished with plants, and to dis- 

 criminate the littoral element due to the action of oceanic 

 currents from the interior forest almost wholly due to frugivorous 

 birds. The recent examination of Christmas Island by the 

 English Admiralty has shown the process of island flora-making 

 in another stage. The plants collected by Mr. Lister prove, as 

 might be expected, to be closely allied to those of Java. But 

 the effect of isolation has begun to tell ; and I learn from my 

 colleague, Prof. Oliver, that the plants from Christmas Island 

 cannot be for the most part exactly matched with their congeners 

 from Tava, but yet do not differ sufficiently to be specifically 

 distinguished. We have here, therefore, it appears to me, a 

 manifest case of nascent species. 



The central problem of systematic botany I have not as yet 

 touched upon : this is to perfect a natural classification. Such 

 a classification, to be perfect, must be the ultimate generalization 

 of every scrap of knowledge which we can bring to bear upon the 

 study of plant affinity. In the higher plants experience has shown 

 that we can obtain results which are sufficiently accurate for the 

 present without carrying our structural analysis very far. Yet even 

 here, the correct relations of the Gymnosperms would never 

 have been ascertained without patient and minute microscopic 

 study of the reproductive processes. Upon these, indeed, the 

 correct classification of the Vascular Cryptogams wholly depends, 

 and generally, as we descend in the scale, external morphology 

 becomes more and more insecure as a guide, and a thorough 

 knowledge of the minute structure and life history of each 

 organism becomes indispensable to anything like a correct deter- 

 mination of its taxonomic position. The marvellous theory of 

 the true nature of lichens would never have been ascertained by 

 the ordinary methods of examination which were held to be 

 sufficient by lichenologists. 



The final form of every natural classification — for I have no 

 doubt that the general principles I have laid down are equally 

 true in the field of zoology— must be to approximate to the 

 order of descent. For the theory of descent became an irresistible 

 induction as soon as the idea of a natural classification had been 

 firmly grasped. 



In regard to flowering plants we owe, as I have said, the first 

 step in a natural classification to our own great naturalist, John 

 Ray, who divided them into Monocotyledons and Dicotyledons. 

 The celebrated classification of Linnaeus was avowedly purely 

 artificial. If was a temporary expedient, the provisional 

 character of which no one realized more thoroughly than him- 

 self. He, in fact, himself gave us one of the earliest outlines of 

 a truly natural system. Such a system is based on affinity, and 

 we know of no other explanation of affinity than that which is 

 implied in the word— namely, common parentage. No one finds 

 any difficulty in admitting that, where a number of individual 

 organisms closely resemble one another, they must have been 

 derived from the same stock. I allow that, in ca«es where 

 external form is widely different, the conclusion to one who is 

 not a naturalist is by no means so obvious. But in such cases it 

 rests on the profound and constant resemblance of internal points 

 of structure. Anyone who studies the matter with a perfectly 

 open mind finds it impossible to draw a line. If genetic rela- 

 tionship or heredity is admitted to be the explanation of affinity 

 in the most obvious case, the stages are imperceptible by which 

 the same conclusion is seen to be inevitable when the evidence 

 is fairly examined, even in cases where at the first glance it 

 seems least likely. 



