LIFE HISTORY OF COLPOMENIA SINUOSA (SYCTOSIPHONACEAE,PHAEOPHYCEAE) IN THE AZORES1

Colpomenia sinuosa (Mertens ex Roth) Derbès and Solier (Scytosiphonaceae, Phaeophyceae) is a common species on the rocky intertidal shores of the Azores, where reproductive gametophytes occur throughout the year. Life‐history studies of this species were carried out in culture, and both sexual and asexual reproduction were observed. Anisogamous gametes fused to form zygotes. The zygotes gave rise to a filamentous prostrate sporophyte generation bearing unilocular sporangia, under both short‐day and long‐day conditions at 15 and 22°C, and to both unilocular and plurilocular sporangia, under the lower temperature condition. Unispores developed into gametophytes, and plurispores gave rise to filamentous sporophytes. Asexual reproduction was carried out by unfused female gametes and asexual plurispores produced from the same gametophyte. Unfused gametes developed into filamentous prostrate sporophytes producing unilocular sporangia in both culture conditions, and unispores released from the sporangia gave rise to gametophytes. Asexual plurispores from field gametophytes, under both culture conditions, developed directly into new gametophytes. The species exhibited three types of life history: a heteromorphic, diplohaplontic; a heteromorphic, monophasic (both with alternation between the erect and filamentous prostrate thalli); and a monomorphic, monophasic.     

Life history of Chnoospora implexa (Chnoosporaceae, Phaeophyceae) in culture

The life history of the brown alga Chnoospora implexa J. Agardh (Chnoosporaceae, Scytosiphonales) from Japan was studied in laboratory cultures. This species showed a heteromorphic and diphasic life history, alternating between erect gametophytes and discoid sporophytes. The gametophytes were dioecious and produced isogametes. The zygotes developed into sporophytes at 20°C under long‐day conditions, which formed plurilocular zoidangia. Zoids released from the plurilocular zoidangia developed again into sporophytes that always formed plurilocular zoidangia at 20°C and 25°C in long‐day conditions, and mainly unilocular zoidangia at 25°C in short‐day conditions. Zoids released from unilocular zoidangia developed into dioecious gametophytes. At 15°C zygotic erect thalli were formed and were revealed to be diploid by microspectrofluorometric measurements of nuclear DNA contents. The development and reproduction of unfused gametes were similar to those of zygotes. Some strains showed a direct‐type life history; gametophytic thalli were produced, but not via a sporophytic phase.     

Morphology and life history of Scytosiphon canaliculatus comb. nov. (Scytosiphonales,Phaeophyceae) from Japan*

Morphology of field material and life history in culture were studied in Scytosiphon canaliculatus (Setchell et Gardner) comb. nov. from northern Japan. Erect gametophytes of S. canaliculatus are cylindrical, tubular, up to 7 mm wide and 40 cm long, and without regular constrictions. S. canaliculatus has pronounced anisogamy and ascocysts accompanied with plurilocular gametangia. The life history of S. canaliculatus showed an alternation between erect gametophytes and crustose prostrate sporophytes bearing unilocular sporangia. Since field sporophytes of S. canaliculatus were found to be identical with Hapterophycus canaliculatus Setchell et Gardner (Ralfsiaceae, Phaeophyceae), it is proposed to transfer H. canaliculatus to the genus Scytosiphon. In the field, gametophytes with plurilocular gametangia appeared in spring and disappeared in summer. Sporophytes with unilocular sporangia were collected in late autumn and winter. Unilocular sporangia were produced at 15°C in short-day culture conditions and unispores developed into erect gametophytes at 5–15°C. It is suggested that the seasonal Occurrence of gametophytes in the field is due to the seasonal formation of unilocular sporangia, which is regulated by temperature and photoperiod.     

Life history and systematic position of the rare brown alga Climacosorus mediterraneus

Cultures of Climacosorus mediterraneus were established with material from Spitsbergen. This species has previously been reported from three widely separated geographic areas: the west Mediterranean, north-west France, and north Norway. Although adapted to temperatures near 0°C, the northern isolate grew well at 15°C which approximates the summer temperature of the southern habitats. The life history proved to be entirely asexual with successive generations bearing unilocular sporangia on the erect filaments and plurilocular sporangia infrequently on the prostrate system. Swarmers of the two reproductive organs gave rise to similar progeny. Chromosome counts revealed equal numbers in somatic cells and unilocular sporangia which substantiates the development observed. The absence of true hairs and the few longitudinal divisions, which only occur in connection with formation of unilocular sporangia and branches, suggest that C. mediterraneus should be assigned to the Pilayellaceae.     

Life history of Japanese Stypocaulon durum (Sphacelariales, Phaeophyceae)

Phenology, morphology, life history and responses to different temperature and photoperiod conditions were studied in Japanese Stypocaulon durum (Ruprecht) Okamura. Erect thalli of the species were collected year-round, but the mature thalli forming either uniloc-ular sporangia or two different types of plurilocular structures (evidently gametangia) on separate thalli were found only in winter. ln culture, an isomorphic life history is suggested for the species, alternating between a sporophyte forming unilocular sporangia and gam-etophytes forming plurilocular macro- (female) and micro- (male) gametangia. Contents of unilocular sporangia were not released, but germinated in situ, developing into erect thalli forming plurilocular gametangia. Macrogametangia released aplanogametes (oospores), but male gametangia appeared to be non-functional, although flagellated cells were once formed in the loc-uli. This is the first report of plurilocular gametangia in the species. Although the species grew well and matured under considerably lower temperature conditions than European Stypocaulon scoparium (L.) Sauvageau, its temperature requirements showed similarity to northwestern Atlantic Stypocaulon species. This supports the notion that northwestern Atlantic Stypocaulon is conspecific with S. durum.     

Life histories of Colpomenia sinuosa and Hydroclathrus clathratus (Scytosiphonaceae, Phaeophyceae) in culture

Life-history studies in culture were carried out on Colpomenia sinuosa (Mertens ex Roth) Derbès et Solier and Hydroclathrus clathratus (C. Agardh) Howe (Scytosiphonales, Phaeophyceae) from Japan. These species showed a heteromorphic life-history pattern with an alternation between erect thalli bearing plurilocular zoidangia and prostrate thalli bearing ectocarpoid plurilocular and unilocular zoidangia. Plurizoids released from erect and prostrate thalli developed into prostrate thalli. Unizoids, however, developed into erect thalli. Prostrate thalli produced plurilocular zoidangia in long-day conditions and unilocular zoidangia in short-day conditions at 10-20°C. Prostrate thalli of C. sinuosa formed ascocysts. Germlings of both species did not grow at 5°C.     

LIFE HISTORY AND HYBRIDIZATION STUDIES ON GIGARTINA STELLATA AND PETROCELIS CRUENTA (RHODOPHYTA) IN THE NORTH ATLANTIC1

Fourteen isolates of the crustose marine red alga Petrocelis cruenta J. Agardh from various localities in the British Isles, France (including the type locality), Spain and Portugal gave rise in culture to dioecious foliose plants identifiable as Gigartina stellata (Stackhouse) Batters although two isolates formed only sterile foliose blades. A total of 145 isolates of Gigartina stellata were also grown in culture from various localities in the U.S.A. (Maine), the British Isles, Iceland, Denmark, France, Spain and Portugal using both carpospores and vegetative blade apices. Two basic types of life history were found among these isolates: a direct-type life history involving the formation of further foliose plants from carpospores, some isolates of which also form spermatangia on the same papillae as the cystocarps; and a heteromorphic-type in which only crustose plants resembling Petrocelis cruenta are formed from carpospores. Only heteromorphic-type life histories were found from Spain and Portugal. Both life history types were found in plants from the U.S.A., the British Isles and northern France. Only direct-type life histories were found in plants from Iceland and Denmark. Some Petrocelis-like crusts derived from field collected G. stellata carpospores and Petrocelis crusts of hybrid progeny formed tetrasporangia in 8:16 h LD, 10° C but not in 8:16 h LD, 15° C; 16:8 h LD 10° C or 15° C; and 10:6.5:1: 6.5 h LDLD, 10° C. The spores thus formed were viable and produced normal dioecious male and female gametophytes. Short day and low temperature conditions appear necessary for tetrasporogenesis. The results from crossing experiments with 32 male and 27 female isolates of the heteromorphic-type derived from both G. stellata and P. cruenta showed that two virtually non-interbreeding populations with a high degree of geographical separation exist in the north-eastern Atlantic. Morphological differences between plants from each population are described. On the basis of culture and crossing results, Petrocelis cruenta J. Agardh is placed in synonymy with Gigartina stellata (Stackhouse in Withering) Batters.     

The biology of Peronospora viciae on pea: laboratory experiments on the effects of temperature, relative humidity and light on the production, germination and infectivity of sporangia

Germination of Peronospora viciae sporangia washed off infected leaves varied from 20% to 60%. Sporangia shaken off in the dry state gave 11–19% germination. Most sporangia lost viability within 3 days after being shed, though a few survived at least 5 days. Infected leaves could produce sporangia up to 6 weeks after infection, and sporulating lesions carried viable sporangia for 3 weeks. Sporangia germinated over the range 1–24 °C, with an optimum between 4 and 8 °C. Light and no effct. The temperature limits for infection were the same as for germination, but with an optimum between 12 and 20 °C. A minimum leaf-wetness period of 4h was required, and was independent of temperature over the range 4–24 °C. Maximum infectivity occurred after 6h leaf wetness at temperatures between 8 and 20 °C. Infection occurred equally in continuous light or in darkness. After an incubation period of 6–10 days sporangia were produced on infected leaves at temperatures between 4 and 24 °C, with an optimum of 12–20 °C. Exposure to temperatures of 20–24 °C for 10 days reduced subsequent sporulation. Sporangia produced at suboptimal temperatures were larger, and at 20 °C. smaller, than those produce at 12–16 °C. Viability was also reduced. No sporangia were produced in continuous light, or at relative humidities below 91%. For maximum sporulaiton an r.h. of 100% was required, following a lower r.h. during incubation. Oospores wre commonly formed in sporulating lesions, and also where conditons limited or prevented sporulation. The results are discussed briefly in relaiton to disease development under field conditions.     

The life history of Ahnfeltiopsis paradoxa (Gigartinales, Rhodophyta) in laboratory culture

The life history of the red alga Ahnfeltiopsis paradoxa (Suringar) Masuda (Phyllophoraceae, Gigartinales) from Japan was completed in laboratory culture. Carpospores isolated from field-collected plants germinated to form circular crusts that were composed of a monostromatic hypothallium consisting of radiating filaments, a polystromatic perithallium consisting of tightly coalescent erect filaments, and hypobasal tissue derived from the hypothallium. The crusts were induced to sporulate by transferring them from short-day to long-day regimes at 15° and 2°C. Each crust produced several nemathecia along 1-4 concentric rings. Intercalary, cruciately or decussately divided tetrasporangia were formed in 4-6 (1-2 at the margin of the nemathecium) successive cells of a single filament of the nemathecia. Tetraspore germlings gave rise to basal discs from which upright axes developed. The upright axes first grew without branches or were sparsely branched and later bore many marginal reproductive proliferations. Procarps and spermatangia were formed in the proliferations on different individuals. Carposporophytes developed on female plants that were co-cultured with male plants. Gonimoblast filaments were formed from an auxiliary cell that fused with a carpogonium. Carposporangia developed from gonimoblast filaments and medullary cells contacted by the gonimoblast filaments. Carpospores were discharged through carpostomes formed in the thickened cortex. Tetraspores were cultured from field-collected crusts of a morphology similar to that of cultured tetrasporophytes. They gave rise to upright gametophytic axes similar in morphology to this species as seen in the field.     

OBSERVATIONS ON THE LIFE HISTORY OF PAPENFUSSIELLA CALLITRICHA (PHAEOPHYCEAE,CHORDARIALES) IN CULTURE1

Papenfussiella callitricha (Rosenv.) Kylin from eastern Canada was studied in culture. Zoids from unilocular sporangia develop into microscopic, filamentous, dioecious gametophytes which produce isogametes in filament cells and few-chambered plurilocular gametangia. Unfused gametes germinate to reproduce the gametophytes. Fusion takes place between a settled (“female”) and a motile (“male”) gamete. The zygote gives rise to a filamentous plethysmothallus that reproduces asexually by zoids formed in thallus cells and in few-chambered plurilocular zoidangia. Erect macrothalli are produced on the plethysmothallus, beginning with the formation of upright filaments. Later on, these filaments become the terminal assimilators of the macrothalli. Further assimilatory filaments, rhizoids, and unilocular sporangia are produced in a branching region at the base of the terminal assimilator. Zoids from unilocular sporangia formed in culture germinate to reestablish the gametophyte phase. Chromosome counts yielded n = 19 ± 3 for the gametophytes, and 32 ± 6 for the sporophyte, both plethysmothallus and macrothallus.     

Temperature Effects on the Onset of Sporulation by Phytophthora ramorum on Rhododendron ‘Cunningham's White’

The effect of temperature and moist period on the onset of sporangia production by Phytophthora ramorum on Rhododendron ‘Cunningham's White’ was examined with misted detached leaves held in humid chambers. Following wound inoculation with sporangia, leaves were pre‐incubated at 20°C for either 24 or 72 h prior to placement at six different temperatures (4, 10, 15, 20, 25 and 30°C). The overall mean moist period required for first occurrence of sporulation over all six temperatures was 3.24 days with the 24‐h pre‐incubation time, compared with 1.49 days for the 72‐h pre‐incubation time. Following 24 h pre‐incubation at 20°C and at an incubation temperature of 15°C, sporangia were first collected from leaves following a 24 h incubation. At 10 and 20°C, sporangia were first collected after 48 h, whereas at 4, 25 and 30°C, sporangia were first collected after 3 days. Following 72 h pre‐incubation at 20°C, sporulation generally occurred within 1 day, even at temperatures such at 4 and 30°C that are suboptimal for sporulation. The highest levels of P. ramorum sporulation were observed at 20°C. P. ramorum formed sporangia on host tissue under moist conditions within the same time frame reported for P. phaseoli, P. palmivora and P. nicotianae, but substantially more slowly than certain other species such as P. infestans. Quantifying moisture and temperature conditions for initiation of sporangia production provides knowledge which leads to a greater understanding of the epidemic potential of P. ramorum.     

Effect of plant growth conditions, plating density, and genotype on the anther culture response of soft white spring wheat hybrids

Ten soft white spring wheat (Triticum aestivum L.) F₁ hybrids were grown under three temperature regimes, and anthers were cultured at two plating densities to investigate the effect of plant growth conditions, plating density, and genotype on embryo induction and plant regeneration. Anthers from plants grown at high temperature (25 °/18 °C) or from plants transferred from low (15 °/12 °C) to high temperature generally produced more embryos and green shoots, with a lower frequency of albinos, than did anthers from plants grown at low temperature. However, plating densities of 10 versus 20 anthers per milliliter, had little effect on anther response. Four of the five hybrids with `Fielder' as the female parent produced more embryos and green shoots than did hybrids with `AC Reed' as the female parent. Received: 12 July 1996 / Revision received: 1 April 1997 / Accepted: 30 April 1997     

A Virus Infection in the Marine Brown Alga Ectocarpus siliculosus (Phaeophyceae)

Laboratory cultures of Ectocarpus siliculosus originating from New Zealand showed a defect in gametangium formation. Nuclear divisions in gametangium initials are not followed by cell wall formation. In the resulting multinucleate cells nuclear DNA increases dramatically, and nuclear membranes disintegrate. Eventually, the entire structure is filled with hexagonal particles of approximately 130 nm diameter. These were isolated and shown by EM to consist of a dense core surrounded by a 3-layered shell. They are released into the culture medium when the host cells burst. Ectocarpus gametes from healthy cultures could be infected by these particles. The resulting partheno-sporophytes developed pathological symptoms, suggesting that the particles are viruses. The expression of the defect is temperature dependent. At 10°C all gametangia are abnormal, while between 15 and 20 °C defective and normal gametangia and gametes are formed on the same plant. Partheno-sporophytes developing from such gametes carry the viral particles expressed in deformed unilocular and plurilocular sporangia.     

MORPHOLOGY AND LIFE HISTORY OF SCYTOSIPHON LOMENTARIA (SCYTOSIPHONACEAE,PHAEOPHYCEAE) FROM THE AZORES1

Morphological and culture studies of Scytosiphon lomentaria (Lyngbye) Link and Microspongium gelatinosum Reinke (Scytosiphonaceae, Phaeophyceae) were undertaken on material collected on the Island of São Miguel, Azores, where both species were commonly found. Erect thalli of S. lomentaria collected in the field were up to 33 cm long and 2.3 mm wide, tubular, hollow, and commonly constricted at intervals. The plurilocular sporangia were positioned in continuous sori on the thallus surface. Ascocysts were present. In the field, M. gelatinosum formed crustose to slightly pulvinate plants, were spongy in texture, and dark brown to black in color, which were circular or irregularly spreading over several centimeters and firmly attached to the substratum. Sessile unilocular sporangia were located in sori on the crust surface. In culture S. lomentaria plurispores developed into Microspongium‐like crustose prostrate thalli that formed unilocular sporangia. Unispores developed into new erect thalli that formed plurilocular sporangia. Sexual reproduction was not observed. In culture, M. gelatinosum unispores developed into erect thalli identical with S. lomentaria. These results are similar to those reported for other areas and suggest the occurrence in the Azorean plants of a monophasic and heteromorphic life history, involving both entities studied.     

Apomeiosis inAcinetospora (phaeophyceae,ectocarpales)

Acinetospora crinita from the Mediterranean Sea has been studied in laboratory cultures. The plants formed monospores and unilocular sporangia. Both monospores and zoids from unilocular sporangia developed to new plants with the same habitus and chromosome number (average ca 47). This indicates that meiosis in unilocular sporangia fails, and that sexuality has been lost in the cultures studied. It is concluded that loss of sexuality is the cause of the great variability and establishment of distinct geographically isolated populations in the genusAcinetospora.     

Reproductive ecology of the freshwater red alga Batrachospermum delicatulum (Batrachospermales, Rhodophyta) in three tropical streams

Batrachospermum delicatulum specimens from three stream segments were analyzed from a tropical region in south‐ eastern Brazil (20°18′– 20°49′S, 49°13′– 49°46′W). Physical and chemical parameters and the spatial placement of thalli were investigated along with the reproductive characteristics of the gametophytic phase. Sequence data of the cox 2‐ 3 spacer region was also utilized to evaluate genetic variation in individuals within and among stream segments. Gametophyte occurred under relatively diverse environmental conditions, whereas thalli abundance was weakly or not correlated to environmental variables within the stream segments. All specimens examined were dioecious. The ratio of male/female plants was relatively low (0.5 to 1.3) and male plants tended to occur as clumps (two or three plants together). High reproductive success was observed, as indicated by the occurrence of 100% fertilized (carposporophytic) female plants. This is similar to previous reports for this and other dioecious species, which is remarkable considering the relatively low proportion of male/female plants. Results support the two hypotheses to explain the high reproductive success in dioecious species. The occurrence of male plants in clumps was evidence for a strict spatial relationship (i.e. male plants located in upstream position of female plants in order to release spermatia, which would be carried by eddies through female plants). In contrast, the occurrence of male and female plants adjacent to each other allowed outcrossing among neighboring plants with intermingled male and female branches, which seemed more applicable to some situations (low turbulence habitats). The cox 2‐ 3 spacer region from the 18 individuals sequenced was 376 bp and the DNA sequence was identical with no base pair substitutions. Likewise, a previous study of another Batrachospermum species showed that the same haplotypes were present in all stream segments from the same drainage basin, even though the stream segments were a considerable distance apart. Short distance dispersal either by small birds or waterway connectivity might explain these findings.     

ECOTYPIC VARIATION IN PHYLLOPHORA PSEUDOCERANOIDES (RHODOPHYTA) ENSURES WINTER REPRODUCTION THROUGHOUT ITS GEOGRAPHIC RANGE1

Responses to temperature and daylength were determined in laboratory culture for isolates of the red alga Phyllophora pseudoceranoides (Gmelin) Newroth et A.R.A. Taylor from Nova Scotia, Iceland, Roscoff (France), and Helgoland (Germany). All isolates grew from 3° to 25° C and survived from -2° or 0° C to 27° C but not 30° C. Reproductive requirements differed between life history phases and isolates. Isolates from Helgoland and Roscoff formed sporangial sori at 3°-20° C, tetraspores at 3°-12° C, and procarps at 10°-20° C, irrespective of daylength. Spermatangia developed at 10°-23° C but only in long days. As the other European isolates, the isolate from Iceland formed tetrasporangia at 3°-12° C, but it had an additional requirement for short days. The Nova Scotian isolate formed sori at 10°-20° C and sporulated at 10°-18° C. When grown plants were transferred from noninductive to inductive conditions, sori were formed after 4 months and tetraspores developed and were shed (1-)3 months later. Procarps formed 1(-3) months after transfer. The phenology of P. pseudoceranoides was studied at Helgoland and Roscoff, where similar seasonal patterns were observed. Plants were perennial, forming new blades from October to June, which degenerated between August and February. In June, reproductive structures (sori, spermatangia, and procarps) started to appear on the new blades. From October to April, mature cystocarps were found. Mature tetrasporangia were observed only in February. The life history of P. pseudoceranoides is regulated by temperature and daylength. Differential effects on the different life history phases all serve to confine the production of spores (both carpospores and tetraspores) to the winter season. Differences in response between isolates from different geographic regions bring about the same effect: spores are shed only in winter. The nature of the geographic boundaries of P. pseudoceranoides is discussed.     

CULTURE STUDIES ON REPRODUCTION OF SPERMATOCHNUS PARADOXUS (PHAEOPHYCEAE,CHORDARIALES)1

The life history of Spermatochnus paradoxus (Roth) Kütz. isolated from the Mediterranean Sea was studied in culture. Meiospores develop to a microscopic stage (microthallus) which at 20°C perpetuates asexually by plurilocular sporangia and formation of new microthalli. At 9°C microthalli act as homothallic gametophytes. Fusion of isogametes results in a diploid microthallus which, after differentiation of an apical cell, leads back to Spermatochnus plants. In addition, gametes develop without fusion to form haploid macrothalli, the further fate of which has not been determined. Chromosome numbers alternate between n = 20 ± 2 in the microthalli and 2n = 41 ± 4 in macrothalli.     

The development of Puccinia hordei on barley cv. Zephyr

Germination of uredospores of Puccinia hordei was similar on cover-slips and on the first leaves of barley seedlings (cv. Zephyr) at 100 % r.h. over the range 5–25 °C, being greatest at 20 °C. At 15, 20 and 25 °C maximum germination was attained in 6 h. No uredospores germinated on coverslips in humidities below saturation. The numbers of pustules which subsequently developed on plants incubated at 5, 10, 15 or 18 °C and 100 % r.h. for varying periods up to 24 h, were directly related to rise in temperature and length of incubation. The time from inoculation to eruption of pustules (generation time) was 6 days at 25 °C, 8 days at 20 °C, 10 days at 15 °C, 15 days at 10 °C and 60 days at 5 °C. Pustule production on inoculated plants which had been kept at 5 °C was rapidly accelerated when they were transferred to 20 °C. Data obtained at constant temperatures were used to predict generation times of the fungus in the field. The productivity of pustules, determined as weight of uredospores, was examined at 10, 15 and 20 °C. Significantly more spores were produced at 15 than at 10 °C and most were produced at 20 °C. The results are discussed in relation to those obtained by other workers and to the development of brown rust in the field.     

ECOTYPIC VARIATION IN CYSTOCLONIUM PURPUREUM (RHODOPHYTA) SYNCHRONIZES LIFE HISTORY EVENTS IN DIFFERENT REGIONS1

Temperature and daylength responses were determined in culture for isolates of the red alga Cystoclonium purpureum (Hudson) Batters from Nova Scotia (NS, Canada), Helgoland (HE, Germany), and Roscoff (RO, France). Most isolates survived temperatures of –1.5°/–2° to 23°C, whereas 25°C was lethal. Only the RO-gametophytes died at 23°C. Optimal growth conditions were 10°–20°C in both long and short days for the NS isolates and 8°–15°C and 8°–18°C at daylengths of >12 h for the RO and HE isolates, respectively. Tetrasporophytes and gametophytes of the NS isolate reproduced at 10°–20°C in long and short days within 5 months. At lower temperatures reproduction was limited or slow. The European isolates formed tetrasporangia at 10°–20°C (HE) or 5°–l8°C(RO), spermatangia at 5°–15°C (HE) or 5°–20°C (RO), and carpospores at 5°–15°C(HE) or 10°–15°C (RO). Short days either blocked or delayed reproduction of the European isolates. The phenology of C. purpureum was studied at Helgoland and Roscoff, where similar seasonal patterns were observed. In early spring, growth was rapid and plants started to form reproductive structures. In summer, tetra-and carpospores were shed followed by degeneration of the upright axes while branched holdfasts persisted. New upright axes and juvenile plants were formed in autumn, but these remained small during the winter months. Published data indicate that the seasonal pattern at Nova Scotia is similar, although the onset of growth and reproduction is delayed until the end of spring. These observations correspond well with the results of the experiments. The life history of C. purpureum is regulated by temperature and daylength. In the eastern Atlantic, the limiting effect of short days confines growth and reproduction to spring and summer. In the western Atlantic, low winter temperatures alone bring about the same seasonal pattern. After plants have reproduced, uprights degenerate in spite of continuing favorable conditions.