222 MR. R. A. ROLFE ON THE APOSTASIER. 
m 
familiar garden Orchids. It is here that the affinities of the 
Orchidee can best be traced, because here ancestral characters 
are less masked by later adaptations. In discussing the affinities 
of any group there is one very important point to be carefully 
borne in mind, viz. the necessity of distinguishing between truly 
ancestral characters (which alone afford evidences of consan- 
guinity or real affinity) and adaptive or developmental characters 
(which may present strong analogies in groups very far separated 
by lineal descent).  — 
Two extreme cases may be mentioned to illustrate this point. 
Ranunculacee presents a number of the strongest analogies with 
Alismacee, and yet the two groups might be traced backwards 
through their various ramifications to the point of divergence of 
the two great branches of the Angiospermese— Monocotyledones 
and Dicotyledones—before the point of contact was reached ; and 
this alone represents the degree of affinity between the two. In 
the same way Asclepiadee and Orchidee present certain simi- 
larities in their economy of fertilization, yet their affinities are 
equally remote. It is therefore clear that organisms, or groups of 
organisms, standing far apart by ties of consanguinity may yet 
tend to approach each other in their adaptive or developmental 
characters if placed for sufficiently long periods under substantially 
similar conditions. Thus adaptations for securing plants against 
long periods of drought take the form of succulence ; or adapta- 
tions for securing the visits of insects frequently take the form 
of irregularity or unequal suppression or development of parts of 
the flower; both producing analogies of structure in very diverse 
groups, 7. e. groups far separated by ties of consanguinity. These 
points are here emphasized because they have not been sufficiently 
recognized by some systematic botanists in discussing affinities, 
and until quite recently were scarcely recognized at all. 
A difficulty may be here supposed to present itself, as to what 
are ancestral and what adaptive characters; but as the two have 
been shown to be so essentially distinct, it is sufficient to establish 
the general principle, premising, however, that, from the very 
nature of the case, no general rule can possibly ever be applied 
toit. Ancestral characters will sometimes be of one kind, some- 
times of another, but always easily recognized as those extending 
with the greatest uniformity throughout a group and subject to 
the smallest amount of variability. Moreover, they are invariably 
most apparent in embryonic structures, becoming most masked 
