. Botany of the living plant. Botany. 392 BOTANY OF THE LIVING PLANT The Ulothricales are relatively advanced in development of their plant-body, owing to repeated cell-division, the products of which remain associated together to form filaments, as in Ulothrix or CEdogonium ; or the filaments may be branched, as in Bulbochaete ; or flattened expansions may be formed, as in Ulva or Enteromorpha. The plants inhabit salt or fresh water, or may even grow- in moist air, as Chroolepiis does. Ulothrix itself, which is â commonly found attached to stones washed by a qxiickly running stream, serves as
. Botany of the living plant. Botany. 392 BOTANY OF THE LIVING PLANT The Ulothricales are relatively advanced in development of their plant-body, owing to repeated cell-division, the products of which remain associated together to form filaments, as in Ulothrix or CEdogonium ; or the filaments may be branched, as in Bulbochaete ; or flattened expansions may be formed, as in Ulva or Enteromorpha. The plants inhabit salt or fresh water, or may even grow- in moist air, as Chroolepiis does. Ulothrix itself, which is â commonly found attached to stones washed by a qxiickly running stream, serves as a simple example. Each un- branched filament consists of a series of discoid cells, each with a zonal chloroplast, and it is attached by a basal rhizoid (Fig. 330, A). Its pro- pagation though varied is rudimentary like its vegeta- tive structure. Zoospores may be produced either singly from a cell or by division of its contents, which escape through an opening of the cell-wall into the water [B). According to the number of the divisions the zoospores may differ in size. Each has four cilia attached to the narrower end of its pear- shaped body [C). After a period of movement they settle, form a cell-wall, and affix themselves to some solid substratum: growing out transversely to their former axis and dividing, each may form a new filament. The. gametes are also produced in a similar way, but the divisions are more numerous, their size smaller, and they bear only tiz'o cilia {E). The gametes, which are all alike in size and form, escape from cells : if those from different filaments meet they coalesce in pairs, the result being a four-ciliate zygote, which soon loses its cilia, settles, and forms a. Fig. 330. Ulothrix zonata. A, young filament with rhizoid r ( A 300). B, portion of filament with escaping zoospores. C, single zoospore. D, formation and escape of gametes. £=gametes. F = conjugation. G=zygote. // = zygote. / = zygote after period of rest. K = zygote after divi
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1919
