September 27, 1900] 



NATURE 



537 



standard unit, like a pound or a pint, but that it is an idea de- 

 pendent upon the subjectivity of individual botanists. For 

 instance, one botanist may regard a certain number of similar 



Slants as all belonging to a single species, whilst another may 

 nd the differences among them such as to warrant the distinction 

 of as many species as there are plants. It is this inevitable 

 variation in the estimation of specific characters which renders 

 it difficult to deal satisfactorily with plants from the statistical 

 point of view. However, the following figures may be regarded 

 as giving a fair idea of the increase in the number of *' good " 

 species of living plants. 



It is generally stated that about 10,000 species of plants were 

 known to Linnreus in the latter half of the eighteenth century, 

 of which one-tenth were Cryptogams ; but so rapid was the pro- 

 gress in the study of new plants at that time that the first enu- 

 meration of plants published in the nineteenth century, the 

 "Synopsis" of Persoon (1807), included as many as 20,000 

 species of Phanerogams alone. Turning now to the end of the 

 century, we arrive at the following census, for which I am 

 indebted mainly to Prof. Saccardo (1892) and to Prof, de Toni 

 who has kindly given me special information as to the Algre : — 



Species of Phanerogams indicated in Bentham and Hooker's 

 " Genera Plantarum " {Durand, " Index," 1888). 



78,200 



19,600 



2,420 



Dicotyledons 

 Monocotyledons 

 Gymnosperms .. 



100,220 

 Estimated subsequent additions (Saccardo) ... 5,011 



Total Phanerogams ... 105,231 



Species of Pteridophyta (indicated in Hooker and Baker's 

 " Synopsis " ; Baker's " New Ferns " and '* Fern Allies "). 



FilicinjE (including Isoetes), about 3,000 



Lycopodinee, about ... ... ... ... 432 



Equisetinse, about 20 



Total Pteridophyta 3,452 



Species of Bryophyta {Saccardo' s Estimate). 



Musci ... 4,609 



Hepaticoe 3»04l 



Total Bryophyta 7*650 



Species of Thallophyta. 



Fungi (including Bacteria) (Saccardo) ... 39,663 



Lichens (Saccardo) ... ... 5, 600 



Algse (incl. 6000 Diatoms) (de Toni) 14,000 



Total Thallophyta 59,263 



Adding these totals together — 



Phanerogams 105,231 



Pteridophyta 3.452 



Bryophyta 7,650 



Thallophyta 59*263 



we have a grand total of 175*596 



as the approximate number of recognised species of living 

 plants. 



These figures are sufficiently accurate to show how vast have 

 been the additions to the knowledge of plants in the period 

 under consideration, and -they afford much food for thought. 

 In the first place, they indicate how closely connected has been 

 the growth of this branch of Botany with the exploration and 

 opening-up of new countries which has been so characteristic a 

 feature of the century. Again, no one can consider these 

 figures without being struck by the disparity in the numbers of 

 species included in the different groups ; a most interesting 

 topic, which cannot, however, be entered upon here. It must 

 suffice to point out in a general way that the smaller groups 

 represent families of plants which attain their numerical zenith 

 in long past geological periods, and are now decadent, whilst 

 the existing flora of the world is characterised by the prepon- 

 derating Angiosperms and Fungi. 



NO. 1613, VOL. 62] 



We may venture to cast a forward glance upon the possible 

 future development of the knowledge of species. Various 

 partial estimates have been made as to the probable number of 

 existing species of this or that group, but the only comprehensive 

 estimate with which I am acquainted is that of Prof. Saccardo 

 (1892). He begins with a somewhat startling calculation to the 

 effect that there are at least 250,000 existing species of Fungi 

 alone, and he goes on to suggest that probably the number of 

 species belonging to the various other groups would amount to 

 150,000 ; hence the total number of species now living is to be 

 estimated at over 400,000. On the basis of this estimate it 

 appears that we have not yet made the acquaintance of half the 

 contemporary species ; so that there remains plenty of occupa- 

 tion for systematic and descriptive botanists, especially in the 

 department of Fungology. It is also rather alarming, in view 

 of the predatory instincts of .so many of the Fungi, to learn that 

 they constitute so decided a majority of the whole vegetable 

 kingdom. 



In spite of the great increase in the number of known species, 

 it cannot be said that any essentially new type of plant has 

 been discovered during the century. So far as the bounds of 

 the vegetable kingdom have been extended at all, it has been 

 by the annexation of groups hitherto regarded as within the 

 sphere of influence of the zoologists. The most notable instance 

 of this has occurred in the case of the Bacteria, or Schizomy- 

 cetes, as Naegeli termed them. These organisms, discovered 

 by Leeuwenhoek 200 years ago, had always been regarded as 

 infusorian animals until, in 1853, Cohn recognised their vege- 

 table nature and their affinity with the Fungi. These plants 

 have acquired special importance, partly on account of the con- 

 troversy which arose as to their supposed spontaneous genera- 

 tion, but more especially on account of their remarkabl e zymo- 

 genic and pathogenic properties, so that Bacteriology has 

 become one of the new sciences of the century. 



Classification. 



Having gained some idea of the number of species which have 

 been recognised and described during the century, the next point 

 for consideration is the progress made in the attempt to reduce 

 this mass of material to such order that it can be intelligently 

 apprehended ; in a word, to convert a mass of facts into a science ; 

 " Filuni ariadneum Botanices est systema, sine quo chaos est 

 Res Herbaria" (Linnaeus). 



The classification of p'ants is a problem which has engaged 

 attention from the very earliest times. Without attempting to 

 enter into the history of the matter, I may just point out that, 

 speaking generally, all the earlier systems of classification were 

 more or less artificial, the subdivisions being based upon the 

 distinctive features of one set of members of the plant. When 

 I say that of all these systems that proposed by Linnreus (1735) 

 was the most purely artificial, I do not imply any reproach : 

 if it was the most artificial, it was at the same time the most 

 serviceable, and its author was fully aware of its artificiality. 

 This system is generally regarded as his most remarkable 

 achievement ; but the really great service which Linnaeus ren- 

 dered to science was the clear distinction which he for the first 

 time drew between systems which are artificial and those which 

 are natural. Recogni.sing, as he did, his inability to frame at 

 that period a satisfactory natural system, he also realised that 

 with the increased number of known plants some more ready 

 means of determining them was an absolute necessity, and it was 

 for this purpose that he devised his artificial system, not as an 

 end, but as a means. The end to be kept in view was the 

 natural classification : " Methodus naturalis est ultimus finis 

 Botanices" is his clearly expressed position in the " Philosophia 

 Botanica." 



There is a certain irony in the fact that the enthusiastic ac- 

 ceptance accorded to his artificial system throughout the greater 

 part of Europe contributed to postpone the realisation of Lin- 

 naeus's cherished hopes with regard to the attainment of a natural 

 classification. It was just in those countries, such as Germany 

 and England, where the Linnean system was most readily 

 adopted that the development of the natural system proceeded 

 most slowly. It was in France, where the Linnean system 

 never secured a firm hold, that the quest of the natural system 

 was pursued ; and it is to French botanists more particularly 

 that our present classification is due. It may be traced from 

 its first beginnings with Magnol in 1689, through the bolder 

 attempts of Adanson and of Bernard de Jussieu (1759), to the 



