4o8 



NA TURE 



[September 30, 1909 



to a narrower field. The organographic systematist realises 

 that in the present state of our knowledge the study of the 

 incidence of selected characters gives more satisfactory 

 results as regards the composition of the higher phyla than 

 repeated aggregation can attain, while the comparative 

 morphologist recognises that, as matters stand, the 

 approximations of organography in respect of types and 

 kinds are more satisfactory than any he can yet offer. 

 Since, however, the progress in one case is outwards, in 

 the other the reverse, a zone of contact is inevitable. This 

 zone, in which the influence of both methods of study is 

 felt, is occupied by those groups immediately higher in 

 value than the natural families of plants, and it is here 

 that discrepancies in the results attained chiefly manifest 

 themselves. These discrepancies take the form of unavoid- 

 able differences of opinion as regards the composition of 

 collections of natural families. If a family A possesses 

 ten characters of ordinal import, whereof it shares eight 

 with a family B and only two with a family C, while the 

 characters combined in A are, as regards B and C, 

 mutually exclusive, the organographic systematist is 

 ordinarily induced to group A and B together and to exclude 

 C from that particular aggregation of families. If, on 

 the other hand, the phylogenist finds that the two characters 

 common to the families A and C are met with in other 

 families, D, E, F, he will ordinarily be led to place A, C, 

 D, E, F in the same higher group from which the family 

 B, notwithstanding its greater general agreement with A 

 than any of the others, must be excluded. This source of 

 discrepancy is, however, less potent than might be ex- 

 pected. When the evidence advanced by either is very 

 strong, the other worker readily accepts it ; in doubtful 

 cases mutual accommodation takes place, the one worker 

 limiting his groups, the other applying his criteria with 

 less rigidity. 



The healthy disregard for formal consistency which 

 admits of adjustments to further practical ends does not, 

 however, alter the fact that a system thus attained can 

 only approximate to the natural arrangement at which 

 both workers aim. Gaps in knowledge may be bridged 

 with histological or teratological aid, or safely crossed with 

 the help of some sudden intuition or happy speculation. 

 But the existence of anomalous types and groups serves as 

 a reminder that much has yet to be learned with regard to 

 living types, while the widest gap in our knowledge of 

 these is a fissure as compared with the chasms that con- 

 front the palaeontologist. : In this the taxonomist of either 

 t>pe finds the incentive to further effort. 



The automatic adjustment of differences due to idiosyn- 

 crasy, and the mutual accommodation of those arising from 

 method of work, still leave considerable want of harmony 

 in taxonomic results to be accounted for. What appear to 

 be rival systems of classification compete for recognition. 

 As each such system professes to be the nearest attainable 

 approximation to the natural arrangement, the evidence of 

 a state of dissension and confusion in the taxonomic field 

 appears to those unfamiliar with systematic work to be 

 incontrovertible. Dissension may be admitted ; confusion 

 there is none. Pictures of the same subject by different 

 artists may be very unlike, yet equally true ; what appear 

 to be rival systems are only manifestations of one. 



It is not difficult to form a conception of this system ; 

 it is less easy to share the conception with others. Let 

 us Imagine a closed space approximately spherical in shape, 

 its surface studded with symbols that mark the relative 

 positions of existing plant-types. Let us imagine the lines 

 of descent of all these types to have been definitely traced 

 and effectively mapped. We find, starting from near the 

 centre of our, sphere, a radiating system of lines; we find 

 these lines to be subject to repeated dichotomy and 

 embranchment which may take place at any point ; we 

 find the resultant lines departing from the original direc- 

 tion at any angle and in any plruie ; we find the nodus of 

 £my indivldu.-il dichotomy , or embranchment capable of 

 serving as the focus of origin for a subsidiary system com- 

 parable in everything except age with the centre of our 

 sphere, and conceivably exceeding in the multiplicity of 

 its ramifications the primary system itself. Some only of 

 our lines reach the symbols that slud our spherical surface, 

 though; every symbol is the terminal of some such line. 

 Here a terminal is fairly isolated, and the line it limits 



NO. 2083, VOL. 81] 



goes far towards the centre with little or no dichotomy 

 or embranchment. Elsewhere our terminals are closely 

 set, the lines they limit running inwards in company until 

 some proximate nodus is reached. Moreover, within our 

 sphere, in the abrupt terminals of various lines we can 

 dimly trace the vestiges of other sphei-es, not always con- 

 centric with our present sphere, once studded with symbols 

 marking the existence of types now extinct. Imagine 

 further the centre of our hypothetical space as not neces- 

 sarily a primary centre, but merely the nodus of some 

 dichotomy or embranchment in a system of which ours is 

 but a residuary fragment. 



As we are practically limited to superficial delineation, 

 an intelligible picture of our system is more than the 

 science of perspective and the art of chiaroscuro can be 

 asked to provide. What is unattainable on the flat is still 

 more impossible in sequence. Serial presentation involves 

 a point of departure ; convenience, predilection, hazard, 

 may dictate what this shall be, and determine the sequence 

 adopted. The result is not a variety of systems, but a 

 series of variants of one system. Considering how complex 

 the problem is, the number of variants is remarkably small. 

 In any case the differences met with are inconsequent ; 

 they do not affect the facts, and the facts alone really 

 count. The trained taxonomist knows that no serial dis- 

 position can indicate, even vaguely, the relative position 

 and import of all these facts. Plane presentation, though 

 more adequate than serial by a dimension, falls short of 

 accuracy ; the surface on which the bulk of the facts may 

 be displayed can have no lateral boimdary. Even if its 

 •presentation on a globe be attempted, the diagram must 

 be incomplete ; many of the points to be shown lie beneath 

 the surface. Convention might overcome the difficulty in- 

 volved in the indication of extinct types, but the diagram 

 would still fail by a dimension to demonstrate the descent 

 of the forms superficially represented. 



Intercourse with the phylogenist, while directly in- 

 fluencing the relationship of the organographic systematist 

 to taxonomy, has indirectly modified his attitude towards 

 the diagnosis and limitation of plant-types. Taxonomic 

 study based on evidence other than descriptive has stimu- 

 lated histological research and fired the anatomist with an 

 ambition to replace by his methods those of organography. 

 It is certainly not for want of industry or care that the 

 success of the phylogenist in the taxonomic field has not 

 also attended the diagnostic work of the anatomist. This 

 failure to replace organographic by anatomical methods is 

 due to the fact that the aualities which make histological 

 evidence useful in generalisation lessen its value in ' dis- 

 crimination. That anatomical characters may be of great 

 use even in diagnosis has been less fully appreciated than 

 it might by those habituated to organographic methods. 

 On the other hand, anatomists who have not benefited by 

 an apprenticeship in descriptive study at times overlook the 

 fact that the value of histological evidence in diagnostic 

 work is indirect. Codification of the scattered results of 

 systematic anatomy has now shown the descriptive worker 

 how useful histological methods are when skilfully and 

 properly used, and has at the same time made it apparent 

 to the anatomist that, in respect of grades lower than 

 ordinal, his methods are more fitted for proof than for 

 demonstration. Their alliance is now cordial and complete. 



While descriptive and anatomical study conjointly make 

 for accurate discrimination, oninion and circumst.-ince com- 

 bine to nrevent uniform delimitation of plant-forms or 

 "species," and no conceivable compromise can overcome 

 this difficulty. With the term " species " is boimd no a 

 double controversy — what idea the word conveys, and what 

 entity the word connotes. Into the first we need not enter: 

 we must assume that our ideas are sufficiently uniform to 

 render the term intelligible. The second we cannot take 

 up here; we must accept the position as we find it, and 

 note, in a snirit of detachment, how in actu;)l practice 

 the systematic botanist does delimit his "species." In 

 doinc this we have to discriminnte between the effect 

 which observed facts produce on different minds, and thnt 

 which different mental states produce on the records of 

 fncts. The results obtained may be essentially identical 

 though arrived at in different ways; as, however, the 

 results are not always uniform, the existence and efTect 

 of these two factors must be carefully noted. 



