FORTIELLA SPHERICA SP.NOV., A NEW BRITISH ALGA

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1 FORTIELLA SPHERICA SP.NOV., A NEW BRITISH ALGA BY DONALD H. MAGGS Department of Botany, Reading (With 5 figures in the text) OF fresh-water algae Fortiella is a rare genus somewhat similar to Chlamydomonas. ItresemblesCarfmainhavingfourflagella, andcoccomonasin having a rigid wall. Tbere is one previous record of the genus in Europe, and there are two little-known Australian species (Pascher, 1927, p. 474). The present species Fortiella spherica was found in an experimental tub behind the Botanical Department of Reading University. Some time before, the water in the tub had been manured with whey from sour milk, and it was consequently rich in organic matter. Fortiella was first found in mid-february wben the water was covered with ice; it occurred in great numbers together with Chlamydomonas and saprophytic flagellates. When discovered, its reproduction had apparently ceased and the resting spores were being formed; attempts to stimulate it to active growth and division by adding more whey failed. As a consequence it has not been possible, so far, to work out the complete life cycle, and only tbe stages subsequent to the liberation of the daughter cells are described. DIAGNOSIS OF FORTIELLA SPHERICA SP.NOV. Lorica ferme globosa, 14/11-16^4 diametro, verrucosa fusee. Flagella 25/X-30/X longitudine. Chloroplastum forma cortinae. Stigma parvum, anterolatere. Pyrenoidum absens. Amylum granulis globosis, multis sed dissipatis. DESCRIPTION A mature individual is shown in Fig. 2. The shell is brown and rigid enough to crack when pressed under a cover-slip. It is usually spherical or it may occasionally bulge to one side; but it is never flattened as in the closely allied genus Fedinopera, nor is tbe shell grooved or otherwise suggesting tbat it is made of two valves. Some tests were carried out to ascertain the composition of the wall. It appears to consist of two materials, (i) a carbohydrate membrane impregnated with (2) a substance whose properties suggest it is bydfated ferric oxide, and to which is due the brown colour and rigidity of the shell. On treatment with potassium ferrocyanide followed by dilute hydrochloric acid, tbe shell turns blue, indicating the presence of a ferric compound. - Treatment witb dilute hydrochloric acid alone, or with oxalic acid causes the

2 i66 DONALD H. MAGGS ferric oxide to dissolve away, and the wall becomes colourless and smooth; acetic acid, on the other hand, does not attack it. Supporting evidence that the shell is impregnated with an iron compound was provided by growing the organism in ferric citrate for a week when a further deposition of brown material on the wall occurred. The soft carbohydrate wall remaining when the ferric oxide is dissolved away may not be a true cellulose, since it does not stain at all with iodine in zinc chloride, nor with iodine followed by 70% sulphuric acid, but it is soluble in concentrated sulphuric acid. In no case did the addition of dilute acid even to a centrifuged mass of cells cause the evolution of a gas, so that calcium carbonate cannot be present in Fig. I. Fig. 2. Fig. I. Starved specimen, with shrunken protoplasm, n, nucleus. X Fig. 2. A typical mature specimen, withflagellaemerging from the pore, e, eyespot; s, shell. X the wall. Pascher's statement in his description of the genus, that the wall is apparently strongly calcified, is thus not general. The shell varies in diameter from 12 to 20/x, most specimens being i4-i6;a in diameter. The protoplasm is naked inside the shell, which it does not completelyfill,and shows no separable membrane when shrunk in glycerin. The four flagella are attached at the pore to a colourless region of protoplasm, the papilla. They are 25-30/ot long, and pull the alga along on a rather wobbly course without rotation. Compared with other organisms of similar size, its speed is rather slow, but it is

3 ' :< Fortiella spherica 167 quite active enough to be abundant even in the surface water. Chloroplast, eyespot, nucleus and two contractile vacuoles can be distinguished. The chloroplast is large and shaped like a cauldron, the mouth towards the pore. There is no pyrenoid, and the chloroplast is loaded with scattered, round starch grains, not more than 4/x diameter, which always obscure tbe other cell structures. Occasionally the chloroplast was deeply lobed as if the protoplasm were beginning to divide. Several such specimens were watched in hanging drop cultures, but none of them divided, and those watched long enough eventually formed normal resting spores. The eyespot (Fig. 3) is red, oval and anterolaterally placed. It is frequently indistinguishable, Fig. 3- Fig. 4. Fig. S- Fig. 3. Youngest stage found. The protoplasm completelyfillsthe membrane, cv, contractile vacuole; e, eyespot; v, the large posterior vacuole. x Fig. 4. Resting spore, p, the thin layer of colourless protoplasm surrounding the rest; s, the shell, which is now smooth, x Fig. 5. Young stage shortly after loss of the posterior vacuole. The wall has just begun to thicken. e, eyespot. x but may become more easily distinguished when specimens are mounted in dilute acetic acid. Tbe nucleus is also diflicult to see, but staining in aqueous cotton blue after bleaching in alcohol showed it as a more deeply stained body. The contractile vacuoles are only shown in Fig. 3. A specimen from a culture which was put in the dark and starved for a week is

4 i68 DONALD H. MAGGS shown in Fig. i. The protoplasm has shrunk considerably, but a few starch grains still remain, although many similar cells in the culture were dying. The nucleus and papilla are more obvious than in the normal state. As has already been said, division had apparently ceased when the alga was found, nor was it ever seen in hanging-drop cultures. However, a series of stages was seen which indicated the probable course of development from a young daughter cell to the mature individual and on to the resting spore. As the development was slow, the sequence was not observed for any single cell. In F. brunnea division is described as longitudinal by Pascher (1927, p. 474). The youngest stage found (Fig. 3) is spherical, and is as big as a typical mature cell. On plasmolysis it is seen to be surrounded by a very delicate clear wall,, which is completely filled by the protoplasm in the living cell. The chloroplast is saucershaped and placed rather on one side of the protoplast; and as it contains few or no starch grains, the eyespot and contractile vacuoles are more easily seen than in mature cells. There is also a large clear vacuole lying away from the papilla. This vacuole is a structure not described at all for the other species of the genus. As development proceeds the delicate wall becomes thicker. Next the large clear vacuole disappears, and the protoplasm shrinks away from the wall all round except where thefiagellaemerge (Fig. 5). As a result the wall can now easily be seen. It is possible that this phase when the vacuole is being lost may be of short duration, as no stages were seen in which the vacuole was intermediate in size. The chloroplast is by now larger and more granular. Then the wall gradually becomes yellowish and acquires the characteristic warts of the adult individual by the external deposition of the ferric oxide. Concurrent with this thickening of the walls the protoplasm slowly enlarges again, this time by increase in quantity, not by the formation of a new vacuole, but it never completely fills the shell. It is loaded with starch grains. Early in March resting spores were of frequent occurrence, and after 12 March the motile stage was never found even in centrifuged concentrates. As the resting condition was assumed, thefiagellawere lost and the alga sank to the bottom of the tub. The chloroplast was packed with starch and usually the protoplasm nearly filled the shells, although some specimens were found where the volume of protoplasm was little more than half that of the shell. Later the wall becomes dark, grey and smooth (Fig. 4). It now gives a blue colour with potassium ferricyanide and not with ferrocyanide, so that it is now impregnated with a ferrous compound, probably ferrous sulphide, the ferric oxide having been reduced under the anaerobic conditions at the bottom of the tub. The grey colour disappears in a few minutes in air, and specimens kept in an open Petri dish were still brown at this stage. The protoplasm shrinks right away from the wall and a layer of clear protoplasm forms around the rest. Treatment with glycerin does not cause a membrane to separate from the shrunken protoplasm. The eyespot and plastid retain their colour. Such stages stain slowly even in strong iodine solution, so that the shell or outer protoplasm must be rather impervious, but drying still causes shrinkage and disorganization of the protoplasm. So far the germination of these spores has not been observed.

5 ., Fortiella spherica, 169 COMPARISON The designation of this alga as a new species seems justifiable on the following grounds. F. spherica differs from the European F. brunnea in the spherical and not long-oval shape of its shell, and in lacking a pyrenoid. It differs from the two Australian species, the shells only of which are described, in its shell being rounded, not, like F. bullina (Playfair) Pascher, emarginate in front, and unlike F. scrobiculata (Playfair) Pascher in being without pits in its shell. Like /. brunnea, F. spherica occurs in water rich in organic matter. Although its life history is incompletely known, the present account has established some new facts about the development and composition of the wall of this little known genus. SUMMARY 1. A new species of Fortiella, F. spherica, is described. 2. An interesting stage in the development of the daughter cells is described, when a large vacuole disappears and the protoplasm contracts away from tbe immature wall. 3. Information is given about the composition and the development of the wall. Finally, I would like to thank Prof. T. M. Harris very much for drawing my attention to tbe alga, and both him and Dr Coulson for their encouragement and stimulating criticism. REFERENCES PASCHER, A. (1927). Die Siisswasser-Flora, Heft 4, Volvocales. Jena.

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