X.1 INTRODUCTION, 



of species, whose spores cannot exist beyond a certain time 

 floating about at tlie mercy of the waves, but must perish 

 if they do not soon find a congenial soil and situation in 

 which to fix themselves and vegetate. Corallines, if occur- 

 ring in abundance, are generally fiital to the growth of 

 other Algae ; and the coral reefs of the Pacific are said to 

 be almost destitute of them. But with due allowance for 

 all these and other modifying causes, we must look to cli- 

 mate as the grand regulator of forms among Algae as among 

 land plants, although it be in a less striking degree, because 

 the temperature of the sea is so much less subject to varia- 

 tion, and ranges within a scale so much shorter than that 

 of the land. It is well known that the majority of the Algaj 

 on our own coasts reach perfection, if not of fruit, at least 

 of foliage, in the summer months ; and that warm summers 

 have a perceptible influence in causing an abundant and 

 a luxuriant growth of particular kinds; and there is even 

 a marked difference between the vegetation of the opposite 

 sides of a sub-marine rock, if one have a sunny and the 

 other a cold exposure, precisely as we notice between one 

 side of a hill and another. These observations, of course, 

 apply with the greatest force to plants growing within the 

 influence of the tide, or in shallow parts of the sea. It is 

 possible, says Lamouroux, that under the Equator tiie 

 plants of the bottom of the ocean, where the temperature 

 is 4° or 5° (41° or 44° F.), have a resemblance to those of 

 the Polar seas, and that those that grow at 100—200 fathoms 

 are allied to those of temperate regions ; but this is mere 

 conjecture, for we know almost nothing of the deep-sea 

 egetation, but we do know that, under ordinary circum- 

 stances, vegetation ceases at a very moderate depth. " On 

 the shores of the British Islands," remarks Dr. GrevUle, 

 " it is easy to perceive that some species, Gelidium corneum, 

 PhyUopkora rabens, and Sph(erococcus corotwpifolius, for 



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