. The algae. Algae. 184 THE ALGAE branched structures from each of which hang 100-150 laminae that bear sporangia in longitudinal folds when they are mature. Apart from the cryptostomata of Saccorhiza and Alaria it has also been suggested that the occur- rence of these sporangia in folds may illustrate how the fertile fucalean conceptacle may have arisen. Such a change would necessitate the development of wedges of sterile tissue in order to divide up the folds, but whether such a change could occur in a relatively differen- tiated thallus is a matter for speculation. The numerous laminae are
. The algae. Algae. 184 THE ALGAE branched structures from each of which hang 100-150 laminae that bear sporangia in longitudinal folds when they are mature. Apart from the cryptostomata of Saccorhiza and Alaria it has also been suggested that the occur- rence of these sporangia in folds may illustrate how the fertile fucalean conceptacle may have arisen. Such a change would necessitate the development of wedges of sterile tissue in order to divide up the folds, but whether such a change could occur in a relatively differen- tiated thallus is a matter for speculation. The numerous laminae are formed by a spUtting process in which a portion of the lamina fails to continue growth whilst the rest goes on growing, and in this manner a weak area is formed from which a split commences. Lessoniaceae : Nereocystis (nereo. Nereis, daughter of Nereus; cystis, bladder). Fig. 105 The plants, which from the re- corded observations appear to be annuals, may attain a maximum length of 90 m., but 50 m. is more usual. This bears a bladder up to 2-3 m. in length^ which has a capacity of several Htres. The long, slender stipe is soUd and cylin- drical below but swollen and hollow above, finally contracting just below the terminal spherical bladder which bears a row of short, dichotomous branches, each giving rise to a number of long, thin laminae. The plant commences with only one blade which divides twice in a dichotomous fashion, thus producing four blades, and these form the centre of activity for the remainder through a pro- cess of sHtting. The spUtting of these four fronds is preceded by ^ Generally much Fig. 104 Postelsia palmaeformis. (After Oltmamis.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Chapman, V. J. (Valentine Jackson), 1910-. London, Macmillan; New York, St. Martin's Press
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Keywords: ., bo, bookcentury1900, bookcollectionbiodiversity, booksubjectalgae
