. The algae. Algae. Fig. 187 Hypothetical life cycle of heterotrichous ancestral form (left) of Cutleria leading to present cycle. Within the Phaeophyceae themselves there would seem to be general agreement that those members with isomorphic alternation of generations probably have some relationship one to the other. The apparently difficult case of Cutleria and Aglaozonia can be explained on the basis of an original heterotrichous ancestor in which the aerial part of the gametophyte persisted and only the basal part of the sporophyte (Fig. 187). In the case of Microzonia (see p. 142) one gene
. The algae. Algae. Fig. 187 Hypothetical life cycle of heterotrichous ancestral form (left) of Cutleria leading to present cycle. Within the Phaeophyceae themselves there would seem to be general agreement that those members with isomorphic alternation of generations probably have some relationship one to the other. The apparently difficult case of Cutleria and Aglaozonia can be explained on the basis of an original heterotrichous ancestor in which the aerial part of the gametophyte persisted and only the basal part of the sporophyte (Fig. 187). In the case of Microzonia (see p. 142) one generation seems to have disappeared completely. There also seems to be some form of general agreement that the orders with heteromorphic alternation (Heterogeneratae) can con- veniently be divided into those that are pseudoparenchymatous (haplostichineae) and those which are truly parenchymatous (poly- stichinae). The real problem in the Phaeophyceae is associated with the origin of the Laminariales and Fucales. It is, for example, possible to imagine a Une of evolution, not only on morphological, the cable type of construction, but also on reproductive criteria, commencing from Ectocarpus-^Castagnea->Chordana-> Chorda-^Laminaria, whilst an alternative origin would be within the ancestral forms of genera such as Dictyosiphon or Punctaria in the Dictyosiphonales. It is also extremely tempting to consider whether the Fucales may not have been evolved from the Lamin- ariales because of the existence of forms such as Durvillea. Indeed recent work by Naylor (cf. p. 207) on Himanthalia and Durvillea has served to strengthen this possibiHty. It has also been suggested that the Fucales might be derived from the Mesogloiaceae (Chordariales), but the evidence produced cannot be regarded as wholly convincing. The principal points are associated with the presence of the apical hairs falling off and giving 316. Please note that these images are extracted from scanned page images tha
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Keywords: ., bo, bookcentury1900, bookcollectionbiodiversity, booksubjectalgae
