286 Scientific Proceedings, Royal Dublin Society. 



XXVI.— ALPHABETICAL LIST OF THE PARASITICAL 

 ALG^ OF THE FIRTH OF FORTH, by GEORGE 

 WILLIAM TRAILL, Joppa, near Edinburgh. 



Communicated by Edward Perceval Wright, m.d. 

 [Read April 17th, 1882.] 



On consulting the various works on British Marine Algse, I 

 have found that comparatively little attention has been specially 

 directed to those species which are parasitical; and, in hopes 

 of the subject proving of interest to the Royal Society of Dublin, 

 I have prepared the following list of the parasites, along with 

 their host plants, which I have observed on the shores of the 

 Firth of Forth — a district sufficiently extensive and prolific to 

 yield interesting results. 



I have endeavoured to give, so far as possible, the periods of 

 duration of the parasites and their host plants, with the times of 

 fructification applicable to the former ; and it will be seen that 

 the parasite invariably attaches itself to a host plant of sufiicient 

 longevity to allow time for the development of its fruit and the 

 escape of its spores, before the usual season arrives for the dis- 

 appearance of the host plant ; and, further, that the life-period of 

 the parasite, irrespective of the time of fruit, is, in the great 

 majority of cases, considerably shorter than that of its host plant. 



The principle of natural selection in the parasite which is thus 

 brought out, will, it is hoped, recommend the list to those who 

 take an interest in this department of botany. 



Parasites 



alphabetically arranged, with periods of 

 duration, times of fructification, &c. 



Host Plants 



in the order of frequency, with periods 

 of duration. 



Asperococcus ecliinatus. 



April to October. Sporangia in 

 Summer. Sometimes on rocks. 



Bangia ciliaris. 



March to August. Fruit in Sum- 

 mer. (" Spring," Le Jolis and 

 Crouan!) 



Cladophora rupestris. All the year. 

 Corallina officinalis. Perennial. 

 Halidrys siliquosa, rarely. Perennial. 



Callithamnion mesocarpum. All the 



year. 



Sphacelaria radicans. Perennial. 



Chsetopteris plumosa, rarely. Peren- 

 nial. 



Khodymenia palmetta, var. nic£eensis, 

 rarely. All the year. 



