Correspondence. 
i 3 l 
“REDUCTION” IN DESCENT. 
To the Editor of the “ Nkw Phvtoi.ogist.” 
Sir, 
The hypothesis of the derivation of a simple structure from a more 
complex one in the course of evolution is nowadays used with great 
freedom in the field of morphological enquiry, and it often enables the 
biologist to understand the existence of types of organization that cannot 
well be interpreted as relatively primitive. In very many cases the 
occurrence of such a “ reduction ” is as certain as any phylogenetic 
conclusion can well be; it is superfluous to mention instances, of which 
many will occur at once to every reader. On the other hand, a too facile 
use of the hypothesis seems to be a danger in various departments of 
current morphological speculation, and the present letter is written with 
the object of calling attention to some aspects of this subject. 
Dealing first with the general question, it will of course be admitted 
that progress from simpler to more complex forms has enormously 
preponderated in evolution. Without going beyond natural selection as a 
cause of modification, it is not difficult to understand why this should be 
so. With certain striking exceptions, increase of bulk gives to the individual 
organism, other things equal, and up to a certain limit, a greater chance of 
competing successfully with its neighbours, and also the power of 
producing a large number of reproductive cells—the two great primary 
factors in the success of a species. But increase in bulk involves increase 
iti complexity of structure, by the necessary division of labour without 
which a large body would become unworkable. Hence we have a great 
primary tendency to increase in bulk and complexity, a tendency which we 
see realised in the history of evolution of the plant-kingdom as a whole. 
Side by side with this, however, other factors come into play. 
Increasing competition for space and food drives some plants into the 
holes and corners left by those which have gained the first footing. The 
adoption of very special modes of life is a further outcome of the com¬ 
petition ; and these, as we see in the case of parasites, endophytes and 
epiphytes—to mention only some of the most general and familiar classes of 
cases—often lead to a very strict limitation or a considerable reduction of 
size and complexity. 
But in all well-established cases of such reduction, we can, without 
much difficulty, put our finger on its special cause, at least we can realise 
in some degree the conditions which have led to the decrease in com¬ 
plexity : and we have 110 reason to believe that there is any general cause 
leading to reduction apart from such special conditions. 
For these reasons it is submitted that in the apparent absence of such 
special cause, the hypotheses of relative primitiveness and of reduction do 
not stand 011 an equal footing. The former has the logically prior claim, 
and must be accepted as a working theory, until good grounds can be given 
for preferring the latter. 
In some quarters, however, there has become apparent a disposition to 
treat the hypothesis of reduction as a mere pawn in the game of mor¬ 
phological speculation, to assume that increase or decrease in complexity 
are equally likely to have occurred, and that the latter can be freely used 
without any special attempt at proof, if it happens to be required by a 
theory based 011 wholly distinct grounds. 
Miss Kthel • Sargaut’s paper on “ The Origin of the Seed-Leaf in 
Monocotyledons,” in the last number of this journal, seems to furnish an 
example of this tendency. 
The paper is of great interest for more than one reason. The real 
relation of the two great groups of Angiosperms—so much alike, and yet 
so well-characterised—is one of the main outstanding problems of com¬ 
parative morphology, and any genuine attempt to solve it claims our close 
attention. At the same time the evidence afforded that detailed and long- 
