The Algae - Phaepophycae - Laminariales - Laminaria

Phylum Thallophyta - The Algae - Phaepophycae - Laminariales - Laminaria  The Laminariales are Phaeophyceae in ,yhich there is a marked alternation of dissimilar generations in which the sporophyte is large and conspicuous while the gametophyte is small and filamentous. Although species of the Laminariales are widely distributed in temperate seas, the bulk of them occur in the colder waters of the Korth Pacific and North Atlantic oceans. Several species are common just below low-tide mark around the British coast. The thallus is large, sometimes exceptionally so, for the order includes the largest of all the sea,yeeds, such as Lessonia and Macrocystis; the latter reaches zoo ft. in length and grows at a depth of 60 to 100 ft. In other species, however, the thallus may be much...

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The Algae - Phaepophycae - Dictyotales - Dictyota dichotoma

Phylum Thallophyta - The Algae - Phaepophycae - Dictyotales  - Dictyota dichotoma These Algae are Phaeophyceae in which a definite alternation of genera­tions occurs and in \yhich the sporophytic and gametophytic plants are morphologically indistinguishable. Sexual reproduction is oogamous, while the organ of asexual reproduction is a non-motile spore termed a tetraspore, so called because only four spores are produced in each sporangium. This is a small order with only a few genera, and \ye shall consider Dictyota dichotoma as our example. Dictyota dichotoma This Alga is common around the coast of Britain, growing in pools between tide-marks. The strap-like thallus is 10 to 20 em. long and consists of rectangular cells arranged in a single layer, with a superficial layer of...

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The Algae - Phaepophycae - Cutleriales - Cutleria multifida

Phylum Thallophyta - The Algae - Phaepophycae - Cutleriales - Cutleria multifida  The Cutleriales are Phae­ophyceae in which there is an alternation of generations be­tween a large upright gamet­ophyte and a small prostrate sporophyte. The gametangia are borne on short filaments arising from the surface layer I of separate gametophyte plants, and the number of gamete cells produced in the male gametangium is considerably greater than those in the female. It is only on the structure of the sex organs that the sexes can be distinguished. The asexual plants give rise to zoosporangia, from which a number of zoospores are liberated. Growth of the thallus is peculiar. The apices of the branches are composed of clusters of uniseriate filaments. These filaments coalesce below to form...

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The Algae - Phaepophycae - Ectocarpales - Ectocarpus

Phylum Thallophyta - The Algae - Phaepophycae - Ectocarpales - Ectocarpus The Ectocarpales are a small group of relatively simple Phaeophyceae in which the thallus is filamentous in its fundamental structure, though very varied in form. In the simplest cases the filaments are entirely free, but in some other forms the lower parts of the filaments are variously aggregated together to form more or less solid bodies, the ends alone remaining free. The vegetative cells in Ectocarpales are shortly cylindrical, containing irregularly shaped chromoplasts with pyrenoids. There is no special apical cell. Growth takes place by the division of an intermediate group of cells in the filament, which form a meristematic zone. Such a method of growth, which is neither apical nor basal, is called intercalary. There...

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The Algae - Phaeophycae

Phylum Thallophyta - The Algae - Phaeophycae The Phaeophyceae are Algae in which an aditional pigment, fucoxanthin, is developed, more or less completely masking the chlorophyll which is also present in the cells. Unicellular types occur, and there are a number of genera in which the majority of the species are filamentous, but the bulk of the species included in this group have a more complex thallus built up of either cellular tissue or of a number of central filaments bound together by mucilage, each of which gives off lateral branches in such numbers that they form a tissue surrounding the central filaments. In such types the central filaments are termed the medulla, while the surrounding tissue is spoken of as the cortex. In the most advanced types the cells of the medulla become modified...

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Phylum Thallophyta - The Algae - CYANOPHYCEAE (Myxophyceae)

Phylum Thallophyta - The Algae - CYANOPHYCEAE (Myxophyceae)  The Cyanophyceae are Algae in which the thallus may be either unicellular or filamentous. It is always enclosed in a gelatinous sheath. The cells possess phycocyanin (blue) and carotin (orange) in addition to chloro­phyll, and the varying proportions of these pigments not only mask the green colour but cause a wide variation of tint from almost pure blue to brown. They occur chiefly in fresh water and on damp surfaces; some are found in the soil, whilst a minority are marine. They constitute the principal vegetation of hot springs, some being able to live in water as high as 85° C. Apart from their interest as the simplest of the Algae they are remarkable for their cytological structure. The cell wall is usually very thin and...

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The Algae - Siphonocladiales - Cladophora

Phylum Thallophyta - The Algae - Siphonocladiales - Cladophora The Siphonocladiales are Chlorophyceae in which each branch of the ' thallus is composed of one or more coenocytes. Though in the simpler members the thallus consists of a single coenocyte and therefore may be comparable with that of the Siphonales, the group as a whole shows a pro­gressive complexity, brought about partly by the development of septa which cut the large coenocytes into smaller ones and partly by the develop­ment of the branching system. Asexual reproduction is by means of zoosporangia in 'which are developed zoospores, or by aplanospores. Sexual reproduction is by the fusion of isogametes. Most of the species are marine and are more characteristic of the warmer temperate and tropical seas than of this country.Many...

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