374 
H. F. Wernham. 
of separate petals to form a tube must be reckoned among the 
actual facts in the history of the flower; Sympetalae have been 
derived from Polypetalae. 1 
We will review briefly some of the arguments in favour of this 
conclusion. First and foremost is the close similarity, in respects 
other than the cohesion of the corolla-members, between various 
polypetalous and sympetalous groups—a similarity which has led 
to the suggestions made in these chapters in regard to the ancestry 
of many of the latter. Thus Ericales have been associated with a 
geranial ancestry, Primulales with a centrospermal ancestry, and 
so on. An extreme case of this similarity, so to express it, is the 
occurrence of polypetalous Sympetalae and of sympetalous Polype- 
talae—significant excepta which defy any sharp distinction between 
Archichlamydeae and Sympetalae. A polypetalous form like Pyrola, 
for instance, conforms in every essential detail with the flowers 
typical of Ericales, save only in its polypetalous character ; while 
an extensive example of the converse—Cucurbitaceae, a sympetalous 
family with unmistakeable and close affinity with anarchichlamydeous 
group—has been exhibited in the preceding chapter. 
Sympetalous forms occur with sufficient rarity among Archi- 
cblamydeae to make the distinction between this group and 
Sympetalae an extremely useful one to the practical systematise 
however unnatural the separation may prove to he ; hut the wide 
area of the affinity over which sympetalous forms occur among 
Archichlamydeae is somewhat striking, for most of the large orders 
are concerned, from the Ranales ( Hcxalobus,Euponmtia , Cisscunpelos, 
Barclay a), upwards. In some families of this series 2 we meet even 
with the paradox of sympetaly or a marked tendency to it, as a 
prevalent character of the family. Such is the case, for example, 
in Crassulaceae (Rosales) in which the petals are usually united, at 
least at the base ( Crassula , Sempervivum, Tillcca), and in some 
genera a definite corolla-tube is a constant feature ( Cotyledon , 
Kalanchce). Pittosporaceae, another family of Rosales, exhibit a 
clear tendency to sympetaly, the union of the petals occurring in 
all stages of completeness, from merely basal cohesion to the 
formation of a tube. In Polygalaceae the cohesion of some, usually 
three, of the petals is an essential feature of the curiously zygomorphic 
flower. The tribe Cusparieae of Rutaceae is characterized by the 
possession of a corolla-tube ; Correa, of the same family, has been 
1 Bentham and Hooker’s name for Archichlamydeze with two 
perianth-whorls. 
2 Apart from Cucurbitaceje (supra). 
