. The algae. Algae. Fig. 70 Ectocarpus. A, E. confervoides, plant ( x 0-44) B, E. tomentosusy unilocular and plurilocular sporangia ( x 100), C, meisporangium, E. virescens. D, megasporangium, E. virescens. E, microsporangium, E. virescens. (A, B, original; C-E, after Kniep.) creasing age, they become much shorter through truncation. The erect filaments of some species have an intercalary growing region, whilst in other species growth is diffuse, but the rhizoids increase in length by means of apical growth. Each cell, which contains one nucleus together with brown, disc or band-shaped chromat
. The algae. Algae. Fig. 70 Ectocarpus. A, E. confervoides, plant ( x 0-44) B, E. tomentosusy unilocular and plurilocular sporangia ( x 100), C, meisporangium, E. virescens. D, megasporangium, E. virescens. E, microsporangium, E. virescens. (A, B, original; C-E, after Kniep.) creasing age, they become much shorter through truncation. The erect filaments of some species have an intercalary growing region, whilst in other species growth is diffuse, but the rhizoids increase in length by means of apical growth. Each cell, which contains one nucleus together with brown, disc or band-shaped chromatophores, possesses a wall that is composed of three pectic-cellulose layers. Generally two kinds of reproductive structures are present, the plurilocular and unilocular sporangia, but some species possess a third type, the meiosporangia. The unilocular sporangia always occur on diploid plants and they give rise, after meiosis, to numer- ous haploid zooids which may either function as gametes or else develop without undergoing a fusion. The sporangia are sessile or stalked and vary in shape from globose to ellipsoid, the mature ones dehiscing through the swelling up of the centre layer in the wall. The plurilocular sporangia, which are either sessile or stalked, range from ovate to siliquose in shape and are to be found on hap- loid or diploid thalli. In E. siliculosus they represent modified lateral branches and arise as side papillae from a vegetative cell in the filament. The plurilocular sporangia are divided up into a number of small cells, each one of which gives rise to a zooid and, when ripe, dehiscence takes place by means of a pore, the contents either germinating directly or else behaving as gametes. The gametes are usually aUke in size but the sex function becomes weaker with age so that relative sexuality is induced, the older and 129. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - colorat
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Keywords: ., bo, bookcentury1900, bookcollectionbiodiversity, booksubjectalgae
