4IO 



NA TURE 



[September 30, 1909 



which it has been subjected, look unlike corresponding 

 fresh material of the same or similar plants, so may trade 

 samples, owing to special treatment, bear little outward 

 resemblance to the same organs and tissues when fresh. 



When material of economic plants is ample another 

 difliculty may be encountered. Domesticated species often 

 undergo perplexing variation. In studying this variation 

 the systematist may have to seek linguistic and archaeo- 

 logical help, and be led into ethnological and historical 

 by-paths. In classifying the forms that such domesticated 

 plants assume he gladly avails himself of aid from those 

 whose capacity for detecting affinities is unusually de- 

 veloped. But even with extraneous assistance the 

 systematist, in this field, sometimes fails to attain final 

 results. He can, however, always pave the way for the 

 student of genetics, whose work involves the study of the 

 " species " as such. As regards forms of economic 

 importance which neither organography nor anatomy can 

 ■characterise, but which the chemist or biologist can dis- 

 criminate, physiological methods are required to explain 

 the genesis or elision of qualities evoked or expunged under 

 particular conditions. 



A highly developed capacity for aggregation, if properly 

 controlled, is also useful in the study of plant distribu- 

 tion from a physiographical standpoint. The systematist 

 •shows his sympathy with phytogeographical needs in two 

 very practical ways. He declines, out of consideration for 

 the geographical botanist, to deal with inadequate material, 

 and for the same reason he refuses, in monographic studies, 

 to be influenced by geographical evidence. The mono- 

 grapher is conscious that if he pronounces two nearly 

 related forms distinct, merely because they inhabit two 

 different areas, he is digging a pit into which the phyto- 

 geographer may fall when the latter has to decide for or 

 against a relationship between the floras of these two 

 tracts. But the fact that, with existing knowledge, 

 uniform delimitation of species is impossible, seriously 

 weakens the value of normal systematic results for phvlo- 

 geographical purposes. The units termed " species " that 

 are most useful in floristic and economic study are often 

 too finely cut to serve distributional ends. When all exist- 

 ing plant-types have been treated on monographic lines 

 the results may with relative safety be used by the phyto- 

 geographer, since errors due to personal equation may be 

 regarded as self-eliminating. As matters now stand, how- 

 ever, the geographical botanist obtains his evidence partly 

 from monographs, partly from floras, and is apt to be 

 misled. Yet even in floristic work the systematist sees 

 that the " species " which it is his duty to 'recognise often 

 arrange themselves in groups of nearly allied forms. 

 These groups, which need not be entitled to sectional rank, 

 while very variable as regards the number of species they 

 contain, are more uniform than species in respect of their 

 mutual relationships. They are therefore more useful than 

 species as units for phytogeographical purposes. In de- 

 fining these groups the faculty for aggregation is essential, 

 and those in whom this faculty is highly developed mav 

 liere be profitably employed, even when their discriminating 

 powers show a certain amount of atrophv. 



The cases, by no means rare, of n-orkers who, with a 

 comparatively poor eye for species, displav great talent in 

 their treatment of genera, afford indirect but striking 

 proof that the faculty for aggregation mav be more highlv 

 developed than its complement, and that the dominance 

 of this faculty may ensure useful results. But the a priori 

 expectation that in dealing with families this dominance 

 should be still more valuable is not borne out bv experi- 

 ence, for in this case it is recognised that aggregation has 

 probably been pushed too far. This error has not been 

 attributable to the faculty for aggregation so much as to 

 the evidence at its disposal ; the corrective has largely 

 teen supplied by the use of anatomical methods as sup- 

 plementary to' organographic data. 



The physiologist in studving processes is not alwavs 

 obligedto take account of the identity of the plants which 

 are their theatres of action. He has at hand manv readilv 

 accessible and stereotyped subjects the identity of which 

 js a matter of cornmon knowledge, and as his experience 

 increases he learns that he may sometimes neglect the 

 identitv even of these. If he asks the systematist to 

 determine some type on which his attention is especially 

 NO. 2083, VOL. 81] 



focussed, the physiologist only does this in order that he 

 may be in a position to repeat all the conditions of an 

 experiment required to verify or modify a conclusion. A 

 passive attitude towards systematic study has thus been 

 created in the mind of the physiologist ; this passivity has 

 been intensified by the fact that the direct help which the 

 physiologist can render to systematic study is limited, 

 l^hysiological criteria are indeed directly applied for 

 diagnostic purposes in one narrow field, where organo- 

 graphy and anatomy are synonymous and inadequate. But 

 if it be true that the diagnostic characters on which the 

 bacteriologist relies belong to some non-corpuscular con- 

 comitant of his organism, this attempt to apply physio- 

 logical characters to systematic ends has failed. In many 

 cases physiological characters do influence taxonomic study. 

 Differences in the alternation of generations, specialised 

 habits connected with nutrition, peculiarities as regards 

 response to stimulation, variation in the matter of pro- 

 tective endowments, admit of application in systematic 

 work, and are constantly so applied in the characterisation 

 of every taxonomic grade. But the evidence as to these 

 characters reaches the systematist through secondary 

 channels, so that the help which physiology renders is 

 indirect, and the passivity of the physiologist remains 

 unaffected. 



This passivity has at last been shaken by the develop- 

 ment of the study of plant distribution from a physio- 

 logical standpoint. The practical value of this study has 

 been affected by the employment of a terminology need- 

 lessly cumbrous for a subject that lends itself readily to 

 simple statement, and by the neglect to explain the status, 

 or verify the identity, of the units included in its plant 

 associations. A reaction against the use of cryptic terms 

 has now set in, and the physiological passivity which has 

 led workers in this field to ignore systematic canons when 

 identifying the units discussed shows signs of disappear- 

 ing. The oecologist, it is true, must classify his units in 

 accordance w^ith characters that differ essentially from 

 those on which reliance can be placed by the systematist. 

 But the characters made use of must be possessed by his 

 units, and the cecologist now realises that, in effecting his 

 purpose, he is as immediately dependent on descriptive 

 results as the economic worker or the get>graphical botanist, 

 and that, if his work is to endure, his determinations must 

 be as precise as those of the monographer, his limitations 

 as uniform as those of the phytogeographer. The needs 

 of the cvcologist are, however, peculiar, and his units 

 must be standardised accordingly. Oncological units are 

 not the groups of species, uniform as to relationship, which 

 the geographical bot^mist requires ; nor are they the prag- 

 matical " species " of floristic and economic work. They 

 are the states, now fewer, now more numerous, that these 

 floristic " species " assume in response to various in- 

 fluences : and cecological associations can only be appre- 

 ciated and explained when all such states have been 

 accurately defined and uniformly delimited. In accomplish- 

 ing this task the faculty for detecting differences is the 

 first essential, and the physiologist has here provided a 

 field of study wherein workers, whose tendency to nicety 

 of discrimination unfits them for normal systematic study, 

 may find ample scope for their peculiar talent, and accom- 

 plish work of real and lasting value. 



We find, then, that the taxonomy of the wider and more 

 general groups is now mainly based on phylogenetic study, 

 and is largely scientific in character and application. The 

 taxonomy of the narrower and more particular groups, 

 based on organographic data supplemented by anatomical 

 evidence, is often somewhat empirical in character, and is 

 largely applied for technical purposes. Among the grades 

 chiefly so applied, tlie " species " is a matter of convenience, 

 variously limited in response to special requirements, while 

 the " family " is a matter of judgment, crystallising slowly 

 into definite form as evidence accumulates. But the 

 " genus " is relatively stable, and, in consequence of its 

 stability, has long been " a thing of dignity." The dis- 

 tinctive air thus imparted to botany is best appreciated 

 when a zoological index is examined. 



The use of scientific names, more precise than popular 

 terms and more convenient than descriptive phrases, facili- 

 tates the work of reference in applied study. These names 

 are accidents which do not affect the taxonomic status of 



