454 WILLIS : MORPHOLOGY OF THE PODOSTBMACEÆ 
and Contortæ, connecting to the Tnbifloræ. Now there is 
little doubt that the Podostemaceæ have some affinities to 
the Saxifragaceæ, as pointed out by Warming (43), and to 
the Lentibulariaceæ, as pointed out by Hooker (18), while 
long ago Gardner (12) pointed out what is possibly their 
nearest relationship, viz., to the Nepenthaceæ and the allied 
orders, such as Sarraceniaceæ. These are tropical orders, 
and the ancestors of the Podostemaceæ were probably also 
tropical. On the whole, therefore, I think that the order 
may well be placed near the cohorts Rosales and Sarrace- 
niales, but the whole question requires much further 
investigation. 
The Qenea^aS E^elistiosi ef the Pedostemaeeæ. 
To sum up in a few words the general bearing of the above 
discussion upon the question of the evolution of these plants 
in reference to the general conditions of life which were 
considered in the introduction, we may perhaps regard it as 
not improbable that the order is descended from tropical 
Dicotyledonous plants rather far back in the evolution of 
the Dicotyledons. These plants may have been aquatic or 
may have been terrestrial ; they probably had creeping 
adventitious roots bearing secondary shoots, and capable, like 
most such roots, of rejuvenescence after any injury to the 
apex ; their flowers were probably erect, regular, with simple 
perianth, insect-fertilized ; their seeds small, ripening in 
the dry season of the year. Gradually we can picture these 
plants taking to life in moving water with a rocky bottom, 
to which their roots would fasten them, and later, as the 
water strain became greater, developing haptera (perhaps by 
some modification of roots) to resist this strain. The roots, 
thus becoming more exposed to the action of light and 
contact, as well as of gravity, would probably, like the 
creeping roots of orchids, &c., tend, under the influence of 
one or more of these causes, to become more or less flattened 
and chlorophyll-bearing. Accompanying this expansion of 
the root and its assumption of assimilatory functions there 
