Summarizing princhipal res lts obtained by our present investigation, we are inclined to think that life-history of Porphyra yezoensis follows a course described below.
Carpospores discharged in spring germinate directly after the discharge. Hence, in summer we usually find them, because of inadequate conditions of environments, remaining as minute fronds throughout the season. However, when external conditions are favourable, they assume the normal course of development even in summer.
These “summer plantlets” initiate an active discharge of monospores as temperature of sea-water approaches to ca. 20°C., and from the monospores thus dischrged develop autumn buds.
The summer plantlets grow on with lowering of water tempetature, discharging continually monospores. The autumn buds too, attaining form of minute fronds, discharge monospores, but this activity is limited in a range of water tamperatures between 20°C. and 15°C.; formation of the monospores is seriously affected by temperatures below 15°C. Consequently, the duration of discharge of the monospores covers a considerably extended period of the year (from September to October at the Bay Usu), and the monospores of delaye I production are considered to develop to December buds and to early winter buds.
With fall of water temperature the formation of the monospores comes to an end, a chief occurrence under such condition being growth of the fronds, which includes formation of male and female sexual cells at the peripheral portions. The carpospores then formed germinate directly after being discharged, and from this fact we consider that these carpospres will further develop to most of the winter buds and to the apring buds.

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The yield of Porphyra of Hokkaido amounts to 140, 000-150, 000 Yen a year. Although 11 species of this genus have been reported from this district, their life-history has never been studied. Therefore we began it with the study of autumn germs of P. yezoensis, the commonest species of the main island of Hokkaidô, in Usu Bay, Iburi Prov., and obtained the following results.
1) Before September 20th, when setting of propagation provision of Porphyra takes place in Usu Bay, many plantlets which are about 11mm in length, and show the characteristics of “Natu-nori” were observed. From their characteristics they can be identified as P. yezoensis U_EDA.
2) When the water temperature is 20°-17°C they discharge monospores.
The growth of the plantlets does not cease with the formation of the monospores, but they continue to grow, discharging monospores continuously.
3) The monospores are 10-13 μ long, germinate soon after they have been liberated. Up to 5-7 cell stage, they divide only by the transverse walls, forming a thread-like body composed of one row of cells. Thereafter they grow up, tracing the developing process of the so-called “Maruba” type of Dr. K_UNIEDA, to an oval or almost round fronds.
4) The optimum temperature for germination of the monospores is 12°-17°C., and 14°-15°C shows the best effect. From this fact the water-temperature in Usu Bay, after the middle September, seems to be in optimum condition for development of the monospores.
5) Two types of the autumn germ, viz. P. yezoensis typc and P. pseudolinearis type, were observed on the collectors of the propagation ground in Usu Bay. The former (about 10mm in length) also discharges monospores in abundance which trace the process of development just like that of “Maruba” type. The latter, however, forms no monospore. Any specimens of this type could not be found before Sept. 20th.
6) From the results mentioned above, it seems to be. very probable the autumn germs of P. yezoensis are generated hom the monospores, and the young Porphyras thus produced dis-charge monospores again. In such a way the number of germs on the autumn collectors in-crease in geometrical proportion.

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