covered at an early age with a vesicular membrane formed by a blistering 

 of the cuticle, fixed by their bases, obovate, with a wide limbus, and 

 finally parted into four sporules. 2. (on distinct plants) solitary, roundish 

 spores (?) scattered among the cells of the surface. — Var. /3. is very much 

 narrower, about a line in diameter at the base, and not a fourth of a line 

 above, dark brown, coarser in substance, with more patent axils, and 

 frequently spirally twisted. 



A very common plant, the most widely dispersed of the genus 

 to which it belongs, being found along the shores of the greater 

 part of the temperate ocean, and also in many intertropical 

 localities. As might be expected, it varies considerably according 

 to the circumstances under which it grows, though without any 

 respect to climate, the most opposite varieties being frequently 

 found on the same shore. The variations appear to result merely 

 from the depth of water at which the plant grows, and the degree 

 of exposure to waves and currents to which it is subjected. In 

 rock-pools near high- water mark and to half-tide level the narrow 

 variety, which sometimes is much narrower and greatly more 

 intricate than our figure represents, is the commoner. Near 

 low- water mark in rock-pools, and among the Laminarice in 

 sheltered bays, the broad variety occurs, of which the average 

 size is represented in the figure ; but some specimens in my 

 Herbarium, gathered by Miss Hincks, at Ballycastle, on the 

 coast of Antrim, are very much wider and proportionably less 

 compound, and bear a considerable resemblance to the tropical 

 D. Schroderi. 



The narrow variety, especially when spirally twisted as it 

 commonly is, looks very like a different species, and is regarded 

 by several continental authors as such. But it is merely distinct 

 in its extreme forms. Intermediate specimens connect it abso- 

 lutely with the broader individuals, and differences in relative 

 breadth are the most uncertain of all characters, especially among 

 the leafy marine plants. The diameter of cylindrical kinds is 

 more constant. 



Fig. 1. Dictyota dichotoma, var. a. 2. The same, var. :— both of the natu- 

 ral size. 3. Portion of the frond with a vertical view of a sorus. 4. A ver- 

 tical section of a sorus. 5. A spore. 6. Portion of the frond, with scattered 

 spores : — all magnified. 



