AN ECOLOGICAL STUDY OF UNDARIA PINNATIFIDA SUR.-V

It has been widly accested that in the species Undaria pinnatifida SUR., two different forms, f. typica and f. distans, have been. However, the necessary characteristics to differenciate the A-form from B-form have not adequately been clarified. This study was carried out for the purpose of finding out the fittest characteristics useful to indentify these forms. The materials and the method of investigation are as follows: (1) The materials were collected from the fronds which were introduced from various original habitats and cultured by hanging-method in Toyohama Harbour, Chita District, Aichi Pref., and also from the fronds in natural habitat at Toyohama and Ono, in the same district. (2) On these materials, biometrical investigations were made on several portions of the same frond, such as the length of frond (L1), the length of stipe (L2), the distance from the lowest margin of blade to the upper end of sporophyll-part (L3), the width of frond (W: the broadest portion in young fronds; W1: the broadest portion of pinnate blade in adult fronds; W2: the same of basal part of blade), the number of pinnate blade (N1), the number of wrinkle of sporophyll (N2), and the shape of sporophyll etc. (vide Figs. 1, 3 ?? 8). Then, these numerical values and interrelations between some of them were compared among the cultured fronds introduced from three original habitats (Toyohama, Ono and Oginohama, Miyagi Pref.), those between the wild and cultured fronds and also those between the fronds of the first and second generations. The results obtained may be summarized as follows: (1) Obvious differences were recognized among the cultured fronds of above mentioned three habitats on the following items: the ratio of L2/L1, the relationship between N1 and L1, the number of wrinkle of sporophyll and the growth rate of frond. (2) As to the comparision of the wild and cultured fronds at Toyohama and Ono, only a few differences were recognized. They are namely, the ratio of W/L1 and the length of frond at the time when the first wrinkle of sporophyll was formed, in the Toyohama-specimens, and the ratio of L2/L1 in the Ono-specimens. As to the difference between the frond of the first and second generation, it was not recognized in the fronds of Toyohama, but was imperceptively seen on the ratio of L2/L1 and the same of W2/W1 in those from Oginohama. (3) Consequently, it was suggested that the shape of fronds at various habitats were distinguishable especially in such characters as follows: (a) the ratio of L2/L1, (b) the rela-tionship between N1 and L1, (c) the length of frond at the time when the first wrinkle of sporophyll was formed, (d) the relationship between N2 and L1, (e) the number of wrinkle of sporophyll, (f) the growth rate of frond. Besides these marked characteristics were scarcely lost by the culture and also were reiterated for some, at least two, generations.