PARASITES ON LAMINARI^I. 153 



up ; and such leaves often afford a rich harvest. The 

 stems and fronds of the Great Oar-weed are very gene- 

 rally clothed with smaller Algse, of which many species 

 are to be obtained only on them. The beautiful Ptilota 

 plumosa is altogether confined to the stems of Laminaria 

 diffitata, and these stems are also the favourite habitat 

 of many other of the more delicate Floridce. Callitham- 

 nion Pluma, a minute but very beautiful species, forms 

 upon them a covering resembling fine crimson velvet ; 

 Delesseria ruscifolia ; Rhodymenia palmetto,, and Poly- 

 siphonia urceolata, are also commonly to be met with. 

 The number of marine animals attached to these weeds 

 is also considerable. Several of the Sertularian and 

 other Zoophytes ; various and beautiful kinds of Bo- 

 tryllus and of other compound Ascidians, as well as 

 several of the Gasteropodous Molluscs, may be collected 

 either on the broad leaves or among the roots of the 

 Laminarise. Two kinds of Patella (P. pellucida and P. 

 Icevis), both remarkable for longitudinal streaks of iri- 

 descent colours on an olive shell, may be found feeding 

 on the LamiuariaD ; the former generally upon the broad 

 leaves, the latter among the fibres of the root, or upon 

 the fleshy stem, and very frequently within the bulb of 

 L. bulbosa. To the labours of these little Molluscs may, 

 indeed, be partly attributed the annual destruction of 

 these gigantic Algse. Eating into the lower part of 

 the stems, and destroying the branches of the roots, 

 they so far weaken the base, that it becomes unable to 

 support the weight of the frond ; and thus the plant is 

 detached and driven on shore by the waves. 



