Abstract:

At the outset the paper begins with a brief discussion of the geographical origin of the

genus Dryopteris. With the cytological data so far available the author presumed that the No-

rthern Hemisphere and possibly Eurasia is the geographical origin of the genus and that the

Eastern Himalayas, China and Japan is the centre of speciation of the genus, and thence has

spread to other continents along several routes. He is also of the opinion that the genus  tends

to evolve the highest grade of polyploidy where it has existed longest. On the other hand, he

pointed out that the production of polyploids may occur most frequently in response to pressures

which a group meets in the course of its migration in space and time, with  the  majority  of

diploids persisting as relics close to the original centre of diversification.

      He then described the progress of the biosystematics of the European and North American

Dryopteris, which has been undertaken through a close cooperation among botanists, cytologists

and phytochemists of different nations. This team is also looking forward to a cooperation with

the Chinese botanists in the study of East Asian species of Dryopteris, so that the relationships

of Chinese species and those of other floras can be understood.

      The term biosystematics had been invented to mean experimental studies of breeding sy-

stems of the species concerned in order to ellucidate their evolutionary relationships.  It stems

from the early researches of Professor Irene Manton whose classical book “Problems of Cytology

and Evolution in the Pteridophyta” (1950) laid the foundation of Biosystematics. Manton was

also the first to introduce the acetocarmine squash  method for staining  chromosomes  in  the

spore-mother-cells at meiosis.

      The lecture was illustrated with diagrams showing in detail the pairing behaviour of the

chromosomes at the metaphase in meiosis and the formation of the polyploidies of different

levels.

      Besides cytological approach two other techniques have been also applied to the systematic

studies of Dryopteris. The first is the comparison of sporoderms  using the scaning  electron

microscope, revealing different ornamentations on the pericine. The second is the study of plant

chemistry, in particular, that of the phloroglucinoles by thinlayer chromatography.

      The remaining far greater part of the paper is devoted to analysing cytologically the Eu-

ropean and North American species of Dryopteris in three groups, showing the lines of experi-

mental work that has resulted in the understanding of their evolutional relationships.