Tvelve-species of the alqa class Eustigmatophyceae were\ud studied by means of light and electron microscopy, with\ud particular reference to structural aspects of the vegetative\ud cells and the flagellar apparatus of the zoospores.\ud \ud The Vegetative cells are shown to have microfibrils\ud (probably cellulose)' in the cell wall (Vischeria stellata),\ud lamellate vesicles in the cytoplasm of all the species\ud observed and a clear connection between the cfiloroplast\ud endoplasmic reticulum and the nuclear envelope only in\ud representatives of the Monodopsidaceae. Microfibrils\ud (probably cellulose) were also found in the cell wall of the\ud tribophycean species Ophiocytium malus.\ud \ud The most significant results on uni- and biflagellate\ud zoospores include the observation of a Golgi body for the\ud first time in a eustigmatophycean zoospore (Vischeria\ud helvetica) and the first reconstruction of the system of\ud flagellar roots in the Eustigmatophyceae (V. stellata). This\ud consists of a rhizoplast and four microtubular roots: roots\ud R1 (3 MTs) and R2 (2 MTs) originate-at basal body B1 and run\ud anteriorly around the flagellar swelling; root R3 (5 MTs)\ud arises between the basal bodies and runs to the posterior end of the cell; root R4 (2 MTs) originates at basal body B2 and curves around the eyespot.\ud \ud For comparison, zoospores of the tribophycean species\ud Heterococcus marietanii and H. protonematoldes were also studied. A system of flagellar roots consisting of a small rhizoplast and three microtubular roots, two directed anteriorly and one posteriorly was confirmed. A double helix was shown to be typical of the transition region of the flagella in-this genus.\ud \ud The few observations on settling cells shoved the\ud withdrawal of the complete flagellar apparatus including the\ud swelling-and the possibility of reformation of the pyrenold\ud in Vischeria from material stored in the spiral vesicles\ud during the motile stage.\ud \ud In preliminary observations on mitosis and cytokinesis\ud it was found that, at early stages, basal bodies appear near\ud the nuclear surface and the chloroplast and the pyrenoid\ud divide. Cytokinesis seems to occur by a cleavage furrow.\ud \ud My reconstruction of the flagellar root system in\ud Eustigmatophyceae shows sufficient similarities with the\ud flagellar, roots of other heterokont algal and fungal classes to justify its, inclusion with them in a single division,the Heterokontophyta. On the basis of this observation and the main ultrastructural features known for these classes,a phylogeny is, constructed for the whole group and the probable characteristics of the, common ancestor are proposed
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