The Botanical Review

Lord, E.

doi: 10.1007/BF02860538pmid: N/A

Cleistogamy—the production of open (chasmogamous—CH) and closed (cleistogamous—CL) floral forms by a species—is widespread among the angiosperms. While the CL flower is autogamous, the CH flower may provide a means for outcrossing. The term “cleistogamy” has also been used to describe other phenomena. A classification of types of cleistogamy is proposed. In this review, a restricted definition of cleistogamy is used to refer to species which show real floral dimorphisms, with divergent developmental pathways leading to CL and CH as well as intermediate floral forms. Reductions in the androecium and corolla are the most common feature of the CL flowers. The structural, developmental, and functional aspects of cleistogamy are reviewed. Evidence is presented to show that the CL flowers have modifications in their development which ensure self pollination. A proposal is made for using this phenomenon of dimorphic flower production as a system for the study of floral morphogenesis, function and evolution.

Held, Abraham

doi: 10.1007/BF02860539pmid: N/A

This monograph surveys the literature on all species of the zoosporic fungal generaRozella (Chytridiales, Olpidiaceae) andRozellopsis (Lagenidiales, Olpidiopsidaceae), which are obligate intracellular parasites of other zoosporic fungi. The special characteristic of these parasites is that their zoosporangium (ZS) fills completely a “compartment,” such as a hyphal segment or a protuberance, in the host thallus. However, the truly distinctive feature of the zoosporangia ofRozella andRozellopsis appears to be the absence of a cell wall of their own. Thus far, this feature has been demonstrated only inRozella allomycis (A. A. Held, Canad. J. Bot.58: 959–979, 1980). However, the fact that in all other species the compartment of the host thallus is occupied just by a single ZS and is separated from the rest of the thallus by one or more septa indicates strongly that the wall which surrounds the ZS belongs entirely to the host. It is argued that since zoospore release is explosive, it is necessary that internal pressure be maintained temporarily in the ZS, and a container made of the host’s cell wall can provide the needed mechanical support only to one naked parasite ZS. (If several naked ZS. filled the container, after the first one released its zoospores the remainder might be unable to do so.) The septation, which the parasite apparently evokes in the host, delimits a ZS which in most cases resembles that of the host, and this phenomenon is referred to as host mimicry. In fact, this septation may in turn bring about the reproductive phase of the parasite. So-called monosporangiate parasite species, which form solitary, nonconjoined ZS, occur in hosts whose own ZS are single (monocentric chytrids) or nonconjoined (e.g.,Pythium spp.), whereas polysporangiate species, which form linear sori of conjoined ZS, occur in hosts which tend to form similarly arranged ZS or gemmae on their own (Allomyces spp., Saprolegniaceae). The naked parasite apparently also stimulates the host wall to form a discharge apparatus-a papilla or tube through which the parasite zoospores are released.

Daghlian, Charles

doi: 10.1007/BF02860540pmid: N/A

The fossil record of monocotyledons is reviewed in order to determine the families actually represented by fossils and their stratigraphic ranges. In providing this information, attention is called to deficiencies and strengths in the record. Most notable is the uneven representation of the four subclasses of monocotyledons. Three distinct phases in the history of monocots can be delineated when the record and ranges of modern families are compared with paleotemperature data. First is a phase of initial radiation and diversification primarily restricted to the Cretaceous and represented by the appearance of a variety of monocotyledonous leaf forms. Second is a phase of modernization of the monocot flora resulting from further development of preexisting Cretaceous forms during favorable climatic conditions during the latest Cretaceous and Paleogene. The third phase is one marked by changes in distributions and expansion of other groups corresponding with climatic deteriorations of the late Paleogene. Some suggestions concerning the limitations of and potential for further research into the fossil record of monocots are presented.