164 
H. F. Wernham. 
standing to that group in much the same relation as Acanthaceae 
to Multiovulatae; in both cases the chief principle underlying advance 
has been efficient seed-dispersal, but each has acquired efficiency 
in a distinct way. 
* * * * 
With a brief summary we may now dismiss the Tubiflorae. 
This large cohort, in spite of the numerous families which it includes, 
is a remarkably natural group, in so far as these families can be 
combined into a single evolutionary tree in the manner we have 
endeavoured to portray. At the root of this tree lies the apocynal 
ancestry, characterised by regular flowers and isomerous androecium. 
These characters are retained in those families which first emerged, 
the Transitional Group ; in the latter the chief tendency is towards 
fruit-specialization, as expressed in schizocarpy. This tendency led 
to the differentiation of two main branches, each determined by 
zygomorphy, but mutually distinguishable on the ground of schizo¬ 
carpy with its attendant tendency to reduction in ovule number. 
This distinction is already well established in the Transitional 
Group, as witness the schizocarpic Nolanaceas and Boraginaceae as 
compared with the non-schizocarpic Hydrophyllaceaeand Solanaceae. 
Convolvulaceae are regarded as terminating the short main trunk of 
the tree before us (see diagram, chapter V), while Polemoniaceae 
represent a branch arising adventitiously, so to express it, from 
the roots. 
The two branches in question give rise to the respective 
stocks of Multiovulatae and Diovulatae. The subsequent branches of 
the latter are but few (see diagram in present chapter), the fruit- 
character being already well-defined. From the former two stocks 
emerge; one, a short one, produces Bignoniaceae, and, by further 
elaboration of the fruit, Pedaliaceas and Martyniaceae; and the 
other becomes the stock of Scrophulariaceae, with relatively 
unspecialized fruit. From the last-named stock three ultimate 
branches arise, leading, 1st, to Lentibulariacese, with extreme 
specialization in structure and habit; 2nd, to Gesneraceae with its 
allies Orobanchaceae on the one hand and Columelliaceae on the 
other, the main feature of this branch being the tendency to 
epigyny; and last, to Acanthaceae with highly complex mechanism 
for seed dispersal, Globulariaceae representing an early-emergent 
side-shoot of the same branch. 
Two broad principles govern the branching of the tree which 
we have described, namely, the advantage of an efficient means for 
