Cadman, Elsie J.

2018-03-29T12:15:03Z

2018-03-29T12:15:03Z

1930

The life-history and cytology of Didymium nigripes have been worked out in detail. The organism grows well in carrot-agar and takes about a fortnight to six weeks to complete its life- history, the time required depending very largely on external conditions.

The spore coat is ruptured by osmotic pressure and the single nucleus then divides karyokinetically, four chromosomes being present. The centrosome arises in the nucleus and passes outwards, leaving behind it the 'Verbindungstuck'. Division of centrosome and Verbindungstuck precede the nuclear division. Nuclear division is followed by division of the protoplast, and two swarm:- cell emerge from the spore coat. The centrosome subsequently functions as the blepharoplast.

After three or four divisions the swarm -cell withdraws the flagellum, 'Verbindungsttick' and blepharoplast and becomes a myxamoeba. The rnyxamoebae fuse in pairs to form the zygote or young plasmodium.

The young plasmodium can ingest swarm-cells and unfused myxamoebae, and can also coalesce with smaller plasmodia. About five or six days after germination, the larger plasmodia exert a distinct attraction on the uninucleate plasmodia in their neighbourhood and these coalesce with them in large numbers,

Nuclear divisions are 'comparatively rare in the young plasmodium. The division is karyokinetic; intracuclear, and no centrosomes are present, Eight chromosomes are formed. The plasmodium increases in size by coalescing with any small plasmodia it encounters,

The stalk of the sporangium is formed by the degeneration of large masses of protoplasm. The wall- and ca._ pilitium probably arise as a result of a chemico-physical action taking place on the surface of protoplasm exposed to air and controlled by the protoplasm itself.

Cleavage of the sporogenous protoplasm and meiosis proceed. simultaneously, The meiosis is typical and consists of the usual heterotype and homo - type divisions, Both divisions are intra-nuclear, without centrosomes and with four chromosomes. In the heterotype division. the chromosomes are U-shaped, in the homotype one they are spherical, The final cleavage into singel spores takes place during the concluding stages of the homotype division.

Didymium Whines is considered to be a more advanced type than Reticularia Lycoperdon, because of the presence of myxamoebae, the fusion of amoeboid gametes, and the formation of a true capillitium,.

http://hdl.handle.net/1842/29029

The University of Edinburgh

Annexe Thesis Digitisation Project 2018 Block 17

The life-history and cytology of didymium nigripes

Thesis or Dissertation

Doctoral

PhD Doctor of Philosophy