234 
H. F. Wernham. 
aside in the same connection, for the leaves of Umbellifloras are 
mostly alternate. Yet stipules of that characteristic interpetiolar 
type, and leaves opposite (occasionally whorled), simple, and with 
entire margins occur without exception in 3,500 species which are 
linked in a more or less close circle of affinity,— i.e., Rubiaceae 
excluding Galieae. This constancy of vegetative characters in so 
large a group is without parallel in the whole series of flowering 
plants, and seems to call for some biological explanation; but the 
writer is unaware that any has been proffered. It may be that 
the stipules, which are often connate into a sheath, exercise an 
important function in bud-protection, in relation to the damp 
tropical conditions under which Rubiaceae nearly always grow ; in 
this case fusion of the stipules might well constitute a “ tendency ” 
to the formation of a much-needed sheath or cap. This contention 
receives some measure of support in virtue of the fact that the 
stipules are rapidly deciduous in many cases; while in Galiese, the 
sole extensive rubiaceous group which inhabits temperate climates, 
interpetiolar stipules do not occur. It is conceivable that the 
stipules of the tropical Rubiaceae, being no longer required for the 
peculiar function which they discharge in a hot damp climate, 
became foliaceous and assumed an assimilatory role in the course 
of evolution of these Rubiaceae of temperate habitats. The variable, 
sometimes large (8 or 9) number of foliar organs in a whorl in 
Galium and its allies, is explicable on the ground of partition of 
originally simple interpetiolar stipules; bipartite and multipartite 
stipules are far from uncommon among the tropical Rubiaceae. 
Interpetiolar stipules occur elsewhere among Sympetalae only 
in Loganiaceae, 1 and, indeed, the latter family have been described 
as Rubiaceae with a superior ovary ; but it must be remembered 
that both families represent relatively primitive groups and display 
considerable diversity in their characters, so that a certain similarity 
between them is not surprising. Epigyny is in this case an important 
critical character, and, on the lines we have followed throughout 
our investigations, we are led to regard Loganiaceae (chapter IV) 
and Rubiaceae as belonging to widely different circles of affinity. 
We can venture no further than the suggestion that this 
peculiar type of stipule determines merely those special lines of 
descent which have led to the two families in question from their 
respective immediate stocks. 
1 So-called “ interpetiolar lines ” unite the two leaf-bases across 
the stem in some Apocynaceae {Taberncrmontana). 
