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Studies on the Adriatic Fucus (Fucus virsoides)
J. Linardić
; Hrvatska
Sažetak
The author of this study, Jo sip Linardic, assistant of the Botanical department of the Faculty of Sciences at the University in Zagreb, began the investigations on the Adriatic Fucus in 1939. Fucus virsoides is an interesting endemic species in the Adriatic Sea, not only because of its ecologic properties, characteristic distribution on the north-east coast, but also because of its systematic value. Whilst many botanists consider it as a specific endemic species, the French algologue Sau- v a g e a u suspects its value as an independent species, and considers it as identic to the Atlantic species Fucus platycar- pus, var. spiralis.
To solve correctly this important question of the systematic value of the Adriatic Fucus, it was necessary to investigate it from the morphological, ecological, chorological and finally systematical point of view. The author had finished his investigations at the end of 1940, and the manuscript was done at the beginning of the hard year 1941. Then began the invasion of Yugoslavia by the enemy’s army of which the author fell a martyr because of his political and national faith, when sentenced to death by a special occupator’s tribunal on 4. VIII. 1941., and so he gave his life for the national deliverance of his country.
The redactor of »Acta Botanica« returned after the war to his position as the chief of the Botanical department of the University; he found the manuscript of Josiip Linardic in Croatian language preserved in the Botanical Institute. As the investigations were performed under his leading, he prepared this manuscript for print, and wrote this summary in English.
I. In the first part of the paper there is shown in detail the morphology of thallus, which is differentiated and consists of three parts: basal disk with rhizoids, rounded stalk (stipes, cau- loid) bilateral leaf-blade of phyloid.
The ramification is typically dichotom-dichopodial. The deviations from the regular dichopodium show only adventive branches, which grow on injured parts of the thallus. »Krypto- stomata« are described in details. The author considers them as organs for absorption of mineral foods. Kryptostomata develop by the reduction of conceptacula changing their reproductive function with that of feeding. In observing the development of the egg, it is found that from the egg develops the embryo by a gradual division analoguely to that known in other species of Fucus. On the thallus of Fucus can often be found prolifications on the bitten parts. These prolifications are described in other species of Fucus and also in the species Fucus virsoides (Meneg- hini, Forti, Vouk). The author could not find out exactly what causes the prolifications, but through some experiments in the aquarium he suspects that the thallus is bitten by a seahedgehog (Paracentrotus lividus). On the bitten parts begins the formation of prolifications the origin of which is shown in details. There are also described utricular anomal formation on the thallus, which have their origin in the schizogenous disruption of the tissue. The anatomical structure of the thallus is shown in details from the point of view of physiologic — anatomical systems. The functional division is still not carried out absolutely, so that some tissue — systems have two or more functions, one of those being of primary, and others of secondary value. Still there can be clearly differentiated the cortical — and vascular — (medular) and mechanical-system. The cortical- system consists of epidermis and cortex. The epidermis is very well and clearly developed in the inside of the cells very well differentiated with chloroplasts on the bottom, and with fuco- san-granules in the upper part of the cells. The epidermis has the function of secreting mucus on the surface.
Immediatly underneath the epidermis is formed the primary cortex with some layers of cells. It has the assimilating function and from it spring out elements of mechanical tissue. In the lower, round parts of thallus is formed the secondary cortex. The primary cortex has its beginning in the epidermis.
The vascular elements are placed in the center, and consist of cylindric, elongated cells. The membranes swell easily forming mucus, and they have pits in the cell-walls, they contain very few plastids and the assimilatory function is reduced, however they contain fucosan. Their function is to accumulate and conduct the assimilates.
The hyphae are mechanical elements. Hyphae are long, thin, with tiny lumen, but with thickened membranes. They are mixed with vascular elements, and are concentrated toward the central rib, and especially in a greater number toward the basal disk. Protoplasts are reduced but still contain fucosan.
With exact comparative investigations the author found out, that there are no differences between northern and southern forms, as J. Schiller states.
II. In the second part of the study is shown in details the ecology of the algae, the relations to the temperature, the salinity, the movements of the sea and the light. The substratum is acting only as a mechanical factor, and not as a physiological one. The highest level of the high tide determines the upper limit of the vegetation-zone of the Fucus, and the lowest level of the low-tide determines its lower one. The Fucus is a typical plant living in the zone of high and low tide. The movements of the sea have a great influence upon the vegetation, so that the samples on unexposed places are always bigger than the ones exposed to the sea waves. The Adriatic Fucus avoides exposed coasts. J. S c h i 11 e r’s statement, that samples from southern coasts are smaller and weaker than the ones from the northern coasts, is not correct. Fucus is a plant adapted to the low and high tide, and dies in a constant culture in the water.
In relation to the salinity Fucus virsoides is an euryhaline species with its optimum inclined more toward the average minimum. According to that, this algae can be defined as mi- kroeuryhalynic typus in the sence of Vouk’s theory of valences. It seeks places with sweetened water.
Concerning the temperature, the Adriatic Fucus is an eurythermal algae with its optimum at the lower temperatures (mikroeurythermal Types). As the Adriatic Fucus is partly a terrestrial plant, for its life is important also the temperature of the air, and this is also a limiting factor, which determines its distribution to the south-western Mediterranean Sea.
Concerning the light, the Adriatic Fucus is an eminently euryphotic i. e. makroeuryphotic algae, because its ecological optimum is nearer to the maximum.
III. In the third part the author discusses the systematic position of the Adriatic Fucus. There is shown the whole history of this algae, which was for the first time described by Vitaliono Donati in 1750 as »virsoide«, according to which Agardh in 1868 gave its first diagnosis under the name of Fucus virsoides. From that time on, this algae has been described under different synonymes, but because of its priority the name of Fucus virsoides has been kept up.
In spite of searching the etymology of the word »virsoide«, the author could neither find the meaning of this word nor anything positive about the etymology of this word.
The author reexamined all the arguments on the basis of which Sauvageau had identified this species with Fucus platycarpus var. spiralis, and found as a result, that none of those arguments could be accepted and that the Adriatic Fucus had a right to be categorized as an independent species, as stated by Agardh. Sauvageau thinks that the Adriatic Fucus has its origin in the oceanic species Fucus platycarpus, which were occasionally distributed in the Adriatic Sea brought from the Atlantic Ocean, and means only a geographical disjunction of the Atlantic species of F. platycarpus var. spiralis. The author point out some essential differences between the species F. platycarpus and F. virsoides:
1. F. platycarpus has the ramification of the dichopodial sympodium, whilst the F. virsoides is a typical and regular di- chopodium.
2. There is a difference in the size between both species. Whilst F. platycarpus has the maximal size of 60—80 cm, F. virsoides grows usually till 20—28 cm. In the same way the segments of F. platycarpus are much wider than the ones of F. virsoides.
3. There is a difference in the receptacula of both species. In F. platycarpus receptacula are placed usually laterally on the shorter lateral branches or terminally in pairs. In F. virsoides receptacula are always placed terminally in pairs.
4. A considerable difference exists between both species in their area of distribution. F. virsoides is usually found on the east coast of the Adriatic Sea mostly to the South till Boka Ko- torska, whilst on the West coats of the North Adriatic it is found very seldom and only till Ancona. In all the other parts of the Adriatic Sea this Fucus is not found, the same as the related species F. platycarpus var. spiralis, which is distributed in the Atlantic coasts northern from Far Oar and Iceland and Canada and on the East from The Canarian isles. The reason that species did not enter Gibraltar and the Mediterranean Sea is probably the high temperature of the air during the summer-months. It is also significant, that F. virsoides, if it originates from the migration of the species F. platycarpus, is not found at all the North-West coasts of the Mediterranean Sea (Italy, France, Spain). The ecovalences of the species F. virsoides prevent its migration in the south Adriatic and Mediterranean Sea.
The author thinks, that these both species were represented by one at the end of the tertiary period and in the early quartery-period. Only later by changing of the paleoclimatic and paleogeographic relations and by the formation of the Adriatic geosynclinalis in the diluvium, and by moving of the climate zone after the ice periods toward the North, began this undivided species its differentiation in two new ones. By the formation of new climatic-relations in the Mediterranean, respectively of the subtropic-mediterranean climate, the continuality of the earlier undivided area of the hypothetic species was broken.
At last the author gives a new, with new arguments enlar- gened diagnosis of the Adriatic Fucus, and considers it as of full value of a separate, morphologically, ecologically and genetically well characterized endemic species.
IV. The author studies the variability of the forms of the Adriatic Fucus, of which he has described several forms and varieties. Analyzing these forms, which have been recently described by Forti, on basis of abundant material from the whole coast from the most northern to the most southern point of the area, he gives lis folowing opinion about all known forms:
f. normalis Schiffner gives an exact diagnosis of the typus. f. normalis major bene evoluta Schiffner, has not the value of a separate systematic unit.
f. normalis basinudus Schiffner. has not the value of a separate systematic unit.
f. normalis partim accedens ad var. subnudam Schiffner, has to be put off as a systematic unit, f. angusta Schiffner, form characterized with narrow segments, well differentiated from the normal form (f. normalis) and never appears mixed.
f. angustior Schiffner has no diagnosis and has to be put off as a separate form.
f. denudata Schiffner, form shows pathological denudation and cannot be considered as a separate systematic unit, var. subnuda Schiffner, the same as the above form has not the value of a separate systematic unit, var. subemersa minor Schiffner, this zonal variety cannot be considered as a separate systematic unit.
var. acutiloba Forti, does not appear on the east coast of the Adriatic Sea, but is a good morphological and geogra- phycal systematic unit.
var. longifructus Forti, good characterized form with double or triple elongated receptacula. var. subvesiculosa Forti, this form with swollen receptacula which are not hollow, cannot be considered as a separate systematic form.
f. australis Sehiffner, according to mentioned signs it cannot be considered as a separate systematic form, f. minúscula Linardić, a small, dwarfy form, only 2—4 cm. the author describes it as a separate form and gives his own diagnosis.
According to that, from all the above mentioned forms only these can be kept as separate ones: var. acutiloba Forti, var. longifructus Forti, f. normalis Scliffner, f. augusta Sehiffner and f. minúscula Linardić. All the other forms have to be off as separate systematic forms either as varieties or as forms.
V. In the last part about chorology of the Adriatic Fucus the author brings an exact list of all till now known localities of this algae, completing this list with his own statements and getting out of all that the area of distribution. Its center is the Trieste, Venetian- and Quarnero-Bay and the Croation Coast. The area elongates till Boka Kotorska on the east coast, and till Ancona on the west coast.
The author gave the exact geographical map of the distribution of this algae in his earlier work: »Contribution to the geographical distribution of the Adriatic Fucus«. (Godišnjak Oceanografskog Instituta II, Split, 1940).
Ključne riječi
Hrčak ID:
152450
URI
Datum izdavanja:
31.12.1949.
Posjeta: 1.716 *