Abstract: Comparative studies on the influence of the temperature factor on the formation and discharge of conchospores of six different species of Porphyra, namely, P. tenera Kjellm., P. suborbiculata Kjellm., P. marginata Tseng et T. J. Chang, P. hemiphylla Tseng et T. J. Chang, P. shangchuanensis Tseng et T. J. Chang and an unidentified species were made and the results presented in the present report. It was found that the range of temperatures in which the conchospores are formed as well as the favorable and optimal temperatures for their formation are unique to each species and are different with different species. With the exception of P. marginata perhaps owing to the lack of sufficient materials available, the demand for higher or lower temperature for the conchospore formation in the species investigated, is generally in agreement with the distribution of these species in the China coast as well as their earlier or later appearance in the same locality. For instance, P. shangchuanensis, at present known only from the Shangchuan Islands off the Kwangtung coast, being southernmost in distribution among these species, requires the highest temperature for conchospore formation (somewhat above 26 ℃). Next in the series is P. suborbiculata, which requires a temperature somewhat higher than 22 ℃. This species occurs principally south of the Yangtze River, and although also found in the Tsingtao region, is killed by freezing temperature, disappearing from the littoral region in the coldest winter months. The other four species are fundamentally northern species and practically limited to the Yellow Sea coast, with the exception of P. tenera which may extend as far south as Amoy, Fukien Province. Two of these four species, namely, P. tenera and P. rearginata, appear earlier than the other two species, similarly requiring higher temperatures for their conchospore formation. It was also found that after formation of the sporangial branchlets, the Conchocelis stage must be subjected to a definite temperature for a certain number of days before conchospores formation could be effected. Although the number of days required is not the same for the species investigated, this varies also with different cultural conditions and with different cultures of the same species. On the basis of large amount of experimental data obtained, it seems that for most species of Porphyra, 10–20 days are required for culturing their Conchocelis-stage (with sporangial branchlets) at favorable temperature in order to form conchospores. Discharge of the conchospores is effected within a certain range of temperature which varies with different species and is related to that of conchospore formation, but somewhat wider in range than the latter, especially in the upper limit of temperature of spore discharge which is always higher than the spore formation temperature.