IN the material collected by Mr Summerhaycs during the O.xford

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1 [ 69] TETRAEDROIDES SPETSBERGENSIS GEN. ET SP. NOV., A NEW ALGA FROM SPITZBERGEN (RESULTS OF THE OXFORD UNIVERSITY EXPEDFITON TO SPITZBERGEN, No. 28) BY B. MILLARD GRIFFITHS, M.Sc, F.L.S. IN the material collected by Mr Summerhaycs during the O.xford University Expedition to Spitzbergen in the summer of 1921, an alga occurred which is apparently a new genus. It was found among the stems of a moss in a crevice of rock on Bear Island, and was associated with a few small diatoms and much vegetable detritus from the plants among whose stems it grew. At first glance the alga resembles a species of Tetracdron, but closer examination shows that the plant is not unicellular but consists of at least two cells and in some cases of even three or four. The thallus of the commoner bicellular type is pyriform, bipyramidal or ellipsoidcil with slightly truncated ends (Figs. 1-7). The exterior walls of the cells are thick but the interior transverse wall is thin. Other two-celled forms are tetrahedral or pyramidal or irregularly polyhedral with very thick exterior walls (Figs. 8-11). As a rule, one or more angles of the polyhedron are distinctly flattened at the apex. More rarely polyhedral thaui consisting of three or four cells occur (Figs. 12, 13); in these cases also, the exterior walls are thick and the interior walls are thin. Vegetative reproduction takes place by a kind of incipient thread formation. One or both cells of the thallus grow out into thin-walled tubular extensions (Figs. 14, 15, 16). The tube divides primarily by a series of constrictions, and each segment is again divided into two cells by the formation of a thin transverse wall. The primary constriction may be complete, in which case the end of the resultant thallus is sharply rounded off, or after constriction has partly taken place, the final division is accomplished by the laying down of a thick transverse wall which sphts and sets the pairs of cells free. In this case the resultant thalli have the truncated apices to which reference has been made. In Fig. 17 is shown an apparently abortive attempt at the foi niation of an incipient thread of about seven cells, of which the tliree lower ha\'e failed to mature. The upper part of the thread shows the

70 B. MiLLARD GRIFFITHS primary constriction of the tube and the thin transverse wall dividing the lower constriction-segment into two cells. In Fig.

2 70 B. MiLLARD GRIFFITHS primary constriction of the tube and the thin transverse wall dividing the lower constriction-segment into two cells. In Fig. i8 is seen a slightly different type of division in which the constriction is partial and the division has been completed by the formation of a transverse wall of considerable thickness. The segment of the initial tube thus cut off is about to be divided by a thin transverse wall whose rudiment can be seen on the left-hand side. The resultant bicellular thallus will have at least one end truncated when the thick transverse wall splits and sets it free. In Fig. 19 is seen a group of three pairs of cells which have been formed by a process of complete constriction into segments, followed by the division of each segment into two cells by the formation of thin transverse walls. One case was observed of what may be a type of asexual reproduction (Fig. 20). One of the cells of the common pyriform or ellipsoidal type appears to be discharging four reproductive bodies through a small lateral pore, but the bodies are not of regular form, nor do they appear to be motile. Although careful search was made, no other example was seen. Each cell of the thallus contains one rather large nucleus. It is provided with a conspicuous nucleolus, and generally lies close to the thin transverse wall. The chloroplasts are small and numerous, more or less oval in shape, and they frequently contain a small pyrenoid (Fig. 7 shows nuclei and chloroplasts; nuclei are also shown in other figures). The systematic position of the alga is very difficult to determine without a further knowledge of its life-history. It is apparently a reduced member of a filamentous group but beyond that little more can be said with certainty. The only alga showing the least resemblance is one brought to my attention by Prof. Fritch, namely Peniococcus NyajtzcB Woloszynska, an alga from the plankton of the Victoria Nyanza (see Woloszynska in Hedwigia, Band 55, Heft. 4-5, p. 205, I9r4; Zellpflanzen Ostafrikas, 1910; Studien u. d. Phytopl. des Viktoriasces, Taf. 7, Fig. 14). It is a thin-walled unicellular alga described as " cylindrices, irregulariter emarginatis, medio constrictis; pyrenoide singulo. Membrana hyalina. Chlorophoris multis. Propagatio divisione transversa." In the dividing stage it bears some resemblance to Tetraedroides forms as seen in Figs, i, 2, 3 and 7, but there is no trace of incipient thread formation and the bicellular state is a phase of division and not a permanent condition of the thallus. The division of Tetraedroides by complete or partial constriction may be a modification of the septation method seen in the Siphono-

3 THE NEW PHYTOLOGIST VOL. XXII, NO. ;, PLATE II 2..1 c a.---,\\ QO.. MILLARI) GRWVVrWA TETR.IIiDROtDES SPET.SBERC;I;MS/S

$If so, Tetraedroides might be considered as a much re duced member of the Siphonoclades, possibly derived from a Rliizocloninm-\\\x ancestor, and bearing a relationship to the group similar to that$

4 Tetraedroides spetsbergensis 71 clades, and the many chloroplasts and pyrenoids and the extrusion of spores from a lateral pore also point somewhat to that group. If so, Tetraedroides might be considered as a much re duced member of the Siphonoclades, possibly derived from a Rliizocloninm-\\\x ancestor, and bearing a relationship to the group similar to that of Pleurococcus to the Ulotrichales. These surmises are, however, far too speculative to use as a definite basis of classification. It might be suggested that this alga, whatever its systematic position may be, is a filamentous form which has assumed the bicellular thick-walled habit as a protection against the rigour of the climatic conditions prevailing in the situation in which it lives. The incipient thread formation and the relatively thin-walled thalli might be considered as summer stages, and the thirk-walled polyhedral forms perhaps as winter stages. DIAGNOSIS. TETRAEDROIDES SPETSBERGENSIS gen. et sp. nov. ThaUus piriformis ellipsoidalis tetrahedralis aut polyhedralis, ex cellulis duabus (scd rarius tribus vel quatuor) compositus. Muri exteriores crassi, interiores tenues. Cellula uninucleata; chloroplastides multas quarum aliquse unam pyrenoidem habent. Multiplicatio vcgetationalis per fuum incipiens quod in geminas cellulas constrictione et muris transversalibus divisum est. Multiplicatio asexualis per sporus quatuor ct nonmotiles qui ex cellula per foramen laterale exeunt. Thallus long /x; lat /.i; crass, max. muri 4^. Habitatio inter muscos in rimis saxorum in Insula Spetsbergensi. DEPARTMENT OF BOT.\NY, ARMSTRONG COLLEGE, UNIVERSITY OF DURHAM. Junuary, EXPLANATION OF PLATE II Camera-liicida drawings, x 650 Figs More common type of thallus. In Fig. 4, the nuclei and chloroplasts are shown; in Fig. 7. ditto, some of the chloroplasts contain pyrenoids. Figs Less common polyhedral thaui; Fig. 10 shows axial view. Fig. 12. Three-celled thallus; empty specimen. Fig. 13. Four-celled thallus; nuclei shown. Figs Incipient thread formation. In Figs and 1,6 the cellcontents of the tubular portions are somewhat plasmolysed. In Fig. 17 c, the upper part of the thread is segmenting by constriction but the transverse walls have not yet appeared. In the lower part, the two lowest cells, b, are apparently aborting, and cell a is completely aborted. Fig. 18. Partial constriction and formation of thick transverse splitting wall at a. At b, thin interior transverse wall is about to form. Fig. 19. Group of pairs of cells formed by complete constrictions alternating with thin transverse-wall formation. Fig. 20. Formation of four spores (?), of which three are already e.xtrudcd fnjin the cell via a lateral pore.

Chlamydomonas. Organelle?

Chlamydomonas. Organelle? Chlamydomonas Organelle? Structure? Organelle? Unicellular thalli typically spherical to subspherical. Eyespot prominent in many species, at cell anterior embedded in chloroplast. Nucleus single and typically