. The algae. Algae. physiology; symbiosis 427 en Nostoc enclosed in the colourless, pear-shaped vesicles that arise from an underground weft of rliizoidal threads. Reproduction by the formation of new vesicles is said to occur only in the presence of the Nostoc. The presence of chitinous material in the vesicular wall suggests a fungal nature for Geosiphon, the vesicles perhaps being galls that are formed on the threads as a result of the presence of the alga. The principal genera taking part in lichen synthesis are Nostoc, Scytonema, Gloeocapsa, Cephaleuros and Trentepohlia. Under normal cond
. The algae. Algae. physiology; symbiosis 427 en Nostoc enclosed in the colourless, pear-shaped vesicles that arise from an underground weft of rliizoidal threads. Reproduction by the formation of new vesicles is said to occur only in the presence of the Nostoc. The presence of chitinous material in the vesicular wall suggests a fungal nature for Geosiphon, the vesicles perhaps being galls that are formed on the threads as a result of the presence of the alga. The principal genera taking part in lichen synthesis are Nostoc, Scytonema, Gloeocapsa, Cephaleuros and Trentepohlia. Under normal conditions the partnership is truly symbiotic, but under abnormal conditions the fungus may become a parasite and devour the algal component. The green bodies which are found associated with the cells of Coelenterates and Radiolarians are usually placed in Torm' genera, Zoochlorella and Zooxanthella (cf. Fig. 225). Most of the species belong to the Cryptophyceae, but in certain of the Coelenterata the motile phases of some of the algae suggest an affinity to the Dino- phyceae, whilst Chlorella (Chloro- coccales) is also regarded as a sym- biont of this group. The non-motile cells are usually found in the peri- pheral layers of the polyp, the larval stages of the host commonly being devoid of the alga. Most of the algal symbionts are known to have a motile phase and hence are ranahle of an inHpnenrlpnt ^^§-225 Symbiosis. Zooxanthellae are capaoie oi an maepenaent in thetissuesofacoeienterate^Po- existence. The function and rela- cilloporabulbosa(x^j^).ec=ecto- tions of these svmhintir alcrap in derm, en =endodermis, ^2= dead uons 01 mese symoiOtlC aigae m zooxanthellae,/^ = fat globule, m^ the coral polyps have been dis- = glands, 5w=structureless lamella, cussed at great length by Yonge ^ = zooxanthellae. (After Yonge.) (1932), and on the whole there would appear to be evidence for a symbiotic relationship, the alga obtaining food from the animal, and the animal oxygen and perhaps
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Keywords: ., bo, bookcentury1900, bookcollectionbiodiversity, booksubjectalgae
