82 
H. F. Wernham. 
two most significant are afforded by the Umbelliferse, which, for 
many reasons, may be placed at the head of the main evolutionary 
line of Archichlamydeae, and by the Composite, the highest type of 
flowering plants. 
(c). A third, and perhaps the most important, subsidiary 
tendency is that of Fusion of Parts. This subserves both the 
fundamental principles. In the first place, space is economized by 
fusion ; economy, too, is effected in material, as is the case with 
the fusion of carpels with receptacle in the Calyciflorae of Bentham 
and Hooker. Material is saved, too, in the shortly filamented or 
subsessile anthers of epipetalous forms. The same primordia, again, 
may suffice for the members of a fusion, as is exemplified in the 
development of the petals from the dorsal portions of the stamens 
observed in certain Primulaceae. 
In the second place, fusion to form a tube is connected with 
the concealment of honey, and so with the principle of adaptation 
to insect-visitors. The primary division of Dicotyledons into 
polypetalous and sympetalous forms therefore becomes significant 
in the light of these principles, and they go far in the direction of 
justifying this division as a truly natural one. 
Other, less general, fusions connected with adaptations to 
insects are seen in the staminal tubes of some forms, e.g., the 
Papilionatae and the Geraniales, and in the adhesions met with in 
various highly specialized groups, such as the Asclepiadaceae. 
In view of the primary importance, in what is to follow, of the 
general considerations to which we have drawn attention in the 
present paper, it will be well, perhaps, to conclude the latter with a 
brief summary :— 
1. The fundamental guiding principles in the progressive 
evolutionary history of the dicotyledonous flower are two in 
number, viz .:— 
(i) . Economy in production of the several items com¬ 
prising reproductive organs. 
(ii) . Progressive adaptation to the reception of insect- 
visitors. 
2. The second of these principles compensates the first for 
the decreased chance of pollination which the 
latter involves. 
3. There are also certain tendencies which subserve these 
two main principles, the most wide-spread being :— 
