422 Mr Rattray on the Distribution of 



other action, so that the spores of the species in question 

 have been enabled to pass the earlier stages of their de- 

 velopment in safety on their often-shifting substrata. As 

 examples of this, on a wider scale, the algoid flora of the 

 opposite (east and west) sides of the May Island, where the 

 crag and tail structure is so beautifully illustrated, may be 

 quoted, while the more or less irregularly fissured and 

 mammillated structure of its northern side also has a facies 

 that contrasts readily in this respect with that of the great 

 ravines and irregular buttresses of its southern margin. 



The occurrence of many Polysiphonice (e.g., P. 2^(^'>^o,- 

 sitica, P. fbrata^ &c.), Callitliamnia (e.g., C. gracillimuni, 

 C. arbiiscula, Cladojjhorce (e.g., C. tmcialis, C. arcta, &c.), 

 Himanthalia lorea, Gigartina mamillosa, and many others, 

 on bare or shaded rocks, is also to be contrasted with the 

 presence of other species, such as Fuci (e.g., F. vesicidosus, 

 F. serratus, F. nodosus, &c.), Fciocarpi (e.g., E. tomen- 

 tosics, E. siliculosus, E. Uttorcdis, E. crinitus), various 

 Ceramia, and even some forms of the elegant Callitliarania 

 (e.g., C. fioridulum), as well as Porphyne, MonostromcB, and 

 Cliylodoxlice on mud-covered rocks and cliffs, as may readily 

 be studied on almost any section of the coast of the 

 mainland, presenting the adequate differences in its physical 

 configuration. 



The presence of species of Enteromorpha (e.g., E. com- 

 pressa) and of Callithamnion floridulum^ among many others, 

 on sand-covered rocks, is no less striking ; whilst the 

 turbidity of the water, which in such circumstances is often 

 so great, especially during the periods of spring tides and 

 storms, that one cannot see beyond a few inches beneath 

 the surface, enables one to realise the often adverse sur- 

 roundings to which such forms can accommodate them- 

 selves. Moreover, the wearing and tearing infiuence 

 exerted on the embedded fronds by the passage of mud 

 and sand as these are carried on by the water has a double 

 influence. For the most part, it is decidedly detrimental 

 to the alga, as always tending to bring about the destruc- 

 tion of its tissues, which, indeed, not uncommonly occurs, 

 more or less lacerated sea-weeds, still adhering firmly to 

 their substratum, being of ordinary occurrence in every 

 estuary and on every shore ; but, on the other hand, this 



