PRESIDENTIAL ADDRESS. 657 
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 disposition 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 boundary. 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 involved 
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 influencing the relation- 
ship 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 stimulated 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 qualities which make histo- 
logical evidence useful in generalisation lessen its value in discrimination. 
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, opinion and circumstance combine to prevent uniform 
delimitation of plant-forms or ‘ species,’ and no conceivable compromise can 
overcome this difficulty. With the term ‘species’ is bound up a double con- 
troversy—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 spirit of detachment, 
how in actual practice the systematic botanist does delimit his ‘species.’ In 
doing this we have to discriminate between the effect which observed facts 
produce on different minds, and that which different mental states produce on 
the records of facts. The results obtained may be essentially identical though 
arrived at in different ways; as, however, the results are not always uniform, 
the existence and effect of these two factors must be carefully noted. 
It is rather unusual to find that workers whose powers of observation are 
equal take precisely the same view of every member of a group of nearly 
allied forms. One, from predisposition or accident, is influenced rather by 
the characters whereby the forms differ ; another is more impressed by those 
wherein they agree. In monographic work especially the same worker may 
find himself alternately more alive to the affinities and more struck by the 
discrepancies among related forms. At one time he feels that his difficulties 
may be best solved by recognising all these forms as distinct, at another he 
1909. UU 
