transparent in the receptacles ; when dry, black. Substance tough, between 

 coriaceous and cartilaginous ; brittle when dry. 



There is something so peculiar in the habit of this species, so 

 different from that of the other members of the restricted genus 

 Fucus, that it seems, even at first sight, to have claims to be re- 

 garded as belonging to another genus. Its branching root, and 

 cylindrical frond are very obvious distinctions, but they are not 

 the only ones. When we come to examine its receptacles more 

 closely, we find, that not merely are they (so to speak) moncecious, 

 each receptacle containing the two kinds of conceptacles, while 

 in Fucus they are dioecious ; but, their cellular structure is widely 

 different, those of the present individuals agreeing much more 

 nearly with the receptacles of Ilalidrys, than of Fucus proper. 

 And it is next to Halidrys that Kiitzing has placed it in his 

 arrangement ; and in my opinion, very properly. 



There is also a striking affinity between the present genus 

 and Xiphophora, Mont., and a nearer analogy, as it appears to 

 me, than with Rimanthalia, with which the learned founder of 

 the former has ably contrasted it. In Xiphophora as in Pycno- 

 phycus, we have the terminal segments of a dichotomous frond 

 converted into receptacles, which receptacles are in both cases 

 monoecious ; and the most striking difference between the genera 

 is, that in Pycnophycus there is an obvious line of demarcation 

 between the frond and the receptacle, while in Xiphophora the 

 receptacles are confluent with the upper branches. Possibly 

 Fucus confluens, Br., may have a similar structme in essential 

 points. 



This plant has a wide range, being found at the Cape of Good 

 Hope, as well as on the shores of southern Europe and of North 

 Africa. In the British Islands, it is much more common in Ire- 

 land than in England, being abundant along our western coasts, 

 at least as far north as Galway. Whereabouts in " the north of 

 Ireland " Dr. Scott met with it, we are not told, but no one has 

 found it recently on the shores of Ulster. 



Fig. 1. Pycnophycus tuberculatum: — of the natural size. 2. A spore. 3. 

 Cross section of a segment of a receptacle, showing a conceptacle cut open, 

 containing parietal spores. 



