The evolution of dimorphism in the pollen and stigmata of members of the Plumbaginaceae has been followed by a return, in some cases, to monomorphism. This has provided an extremely useful tool for the elucidation of genetical, genecological, phytogeographical and evolutionary problems. In the search for a comparable situation in other families, the neglected and ambiguous account of pollen dimorphism in 'Faramea' described by Fritz Müller and accepted by Charles Darwin has been reinvestigated.
Examination of the pollen of genuine Faramea, the tracing of Müller's herbarium material and the study of new collections has shown that Rudgea jasminoides (Cham.) Muell.-Arg. (Rubiaceae) is the species involved and that pollen dimorphism associated with heterostyly has evolved in the Rubiaceae in a manner quite comparable with that in the Plumbaginaceae. The difference between the two pollen forms of a single species of Rudgea is as great as that which distinguishes some genera or higher taxa yet it may have a simple genetical basis. Occurring as it does in a genus of woody tropical plants (and possibly being present in related genera with a similar habit), this dimorphism may be an important aid to the study of the history and distribution of tropical forest floras, of which there is little fossil record.
There are several sources of potential error in calculating the concentration or energy value of floral nectar. Errors resulting from confusing data become substantial with increasing concentration. The different methods of expressing sugar concentration are here clarified, and the correct methods of converting from one to the other are provided. Refractometers in use in field studies usually read on a weight per total weight basis; this is recommended as the mode of statement. The perils of ove
rsimplifying conversions from this mode, as is often done, are pointed out.
An effusion of books and articles on pollination biology has appeared recently, showing a renewed interest in this area of reproductive biology that has strong significance for the continuous evolution of seed plants. Consequently, a comprehensive review is not possible in this paper; topics have been selected and a restricted number of examples given. New findings in "classical" pollination scenarios are reported, while newer topics include the chemistry of nectar in relation to phylogeny and p
ollinator types. The formation of "pollination ecotypes" within species is considered but the obstructive influence of "phylogenetic constraint" on close adaptation between flower and pollinator is illustrated. Collaboration with other kinds of biologists will be important. Relevant post-pollinatory events are considered briefly. Some of the requirements for pollination study at population and ecosystem levels, including those of pollinator sharing and mimicry, are reviewed. Botanic gardens and field stations will play a prominent role in these endeavors.