84 THE BOTANICAL MAGAZINK lv.-i. xxxiii. no. m 



were covered by the single species. It was in May and June that 

 we found Urospora penicilliformis mixed with Ulothrix. (Text- 

 fig. 2). 



The level of the Por/j/zrra-forraation on the experiment 

 block appears to me, after my experiences for continuous vears 

 at the reef, to be much lower than it has been expected. At 

 the height where the block surface w^as completely drained in 

 the low water time, especiallj' on the sloping sides, not a single 

 frond of Porphyra could be found. This is not the case in the 

 natural substrata. (Text-fig. 2). 



It is known to us that too much smoothness of the sub- 

 stratum is not fitted for the growth of the algae^-*. Rough 

 surface of hard and compact stone is the best substratum for 

 any alga. Certain algae, for instance, Gloiopeltis, Lithoderma, 

 Corallina, etc., which have prostrate primary thalli can grow 

 on smoother surfaces than others. This character is utilized by 

 our fishermen for the culture of Gloiopeltis for which a smooth 

 andesite masses are chosen. 



The surface of the experiment block was therefore smoothed 

 as I have thought it suitable for the plant. The fact that the 

 Porphyra in Tokyo Bay is invited to bamboo twigs, induced 

 mc to presume that the " rock-porphyra " may also grow on 

 fairly smooth surface. 



From the result I have obtained in the experiment block, I 

 am tempted to conclude that the " roek-porphyra " can not 

 thrive on such smooth surface of substratum as the " twig- 

 porphyra " can. This difference of ecological character may per- 

 haps be due to the amount of Diatoms and other microscopical 

 organisms attached to the substratum beforehand. In the 

 quiet waters, gelntinuous coatings of the so-called " dirts " 

 on the bamboo twigs may be thick enough to hold the spores^'. 

 On the open coasts, the rocks will hardly be covered with such 

 thick coatings of micro-organisms. A smooth substratum fron- 

 ting to rough water would be logically dillieult for the algal 

 spores to take their anchorage on it. More vegetation of 



1) YkndO: On tlie cultivation of Seaweeds, p. 117. 



2) Ditto. p. 1T,». 



