The Life History of Some Species of the Scytosiphonales

Abstract

was transferred to a glass vessel (6.5cm.8.0cm.) containing 180 ml. of medium.Sexual reproduction was examined by mixing swarmers liberated from different individuals under a microscope.Zygotes could be easily detected by two eyespots which were retained for a few days.They were isolated by removing unfused gametes which attached themselves to the glass slide together with the zygotes, with a fine needle or a micropipette under a microscope.For a single plant culture, the 5.vlO-day-old germlings attached to the glass slide were isolated with a micropipette and transferred to the culture test tube (2cm.13cm.)containing IO ml. of medium.The culture medium ttsed in this study was PESI, a slight modification of PRovAsoLi's ES medium and it was replenished at intervals of about 3e days.Cultures were grown in.freezer-incubators illuminated with cool white fluorescent lamps (ca.1500BOOO lux) at specified temperatures and photoperiods in the following combinations. PhotoperiodNumberofincubator TeMPeratUre(OC) (Hrlight-Hrdark)No.1 10 14-10 No.2 I2 '10-14 No.3 14 14-10 No.4 14 10-14 No.5 18 16-8 These variables were selected to correspond approximately to intertidal conditions at the area of Muroran.During winter (December to February) water temperature was measured to range from 3 to 70C. and photoperiod was a shortday condition, ranging from 9 to 11 hours o"ight.In this season, the fronds of Saytosiphon, Petalonia and Co(lbomenia grow well in nature.However, they grow poorly under conditions of 5aC and a IO-hr photoperiod in the laboratory culture. Conditions ofNo. 1 and No. 3 correspond to those of April and May at Muroran, when Saytosiphon and Coipomenia plants thrive most luxuriantly.Conditions of No. 2 aRd No. 4 correspond to those of October and November when ralfsioid plants with unilocular sporangia of Saytosil2)hon and Petalonia are found in nature.Conditions of No. 5 correspond to those of the end of June and July-August when the fronds of Saytosiphon and Co(Pomenia disappear in nature.For the cytological observation, small pieces of the fronds or young germlings were fixed in the fixative of 1:3 acetic alcohol during night-time in nature and dark-period in culture.The staining of chromosomes was made by application of aceto-iron-haematoxylin-chloral hydrate method (YABu and ToKiDA, 1966).