208 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



very simple structure, though evidently connected in an un- 

 broken chain with others which form submarine forests, and 

 vie in habit with many a Phgenogam, and in some cases exhi- 

 bit an approach to exogenous growth. 



191. In this division, as in the last, it is possible that certain 

 of the lower cellular forms of AlgJB, as well as the filamentous, 

 may really, in a truly natural system, be entitled to a place 

 here ; but, inasmuch as artificial distinctions are inseparable 

 from any systematic arrangement, even though we might have 

 a glimpse of the truth ourselves, it would, probably, be im- 

 possible to put it forward in such a shape as to be practically 

 useful. In the present condition of Algology, a large number 

 of those species which have been sufficiently studied in their 

 place of growth, are known to be either monoecious or dioecious, 

 and the day is probably not far distant when even amongst 

 the simpler Algae, spermatozoids, or their representatives, will 

 be found to prevail universally. I say representatives, because 

 in many Melanosperms there are two kinds of zoospores pro- 

 duced in different organs, both of which are fertile, and the 

 genus Cutleria seems to lead directly to these, in which, 

 though two kinds of bodies are produced, absolutely similar 

 in form, though not in size, to those of StilopJiora, one only 

 has at present been ascertained to be fertile. The repro- 

 ductive body here is a zoospore, and it is probable that the 

 other body is a spermatozoid.* If not a true spermatozoid, 

 then, it is at least representative. 



192. Melanosperms occur in all parts of the world. Scy- 

 tothalia Jacquinotii, and Adenocystis Lessoni, attend 

 Iridoea micans in Cockburn Island, while Desniarestia acu- 

 leata, and Laminaria saccharina extend as far as 73° or 74" 

 N.L. If the higher parts of the Northern Ocean abound in 

 Laminariw, the warmer seas support multitudes of Sargas- 

 sum, while the southern have their species of Maerocystis, 

 D'Urvillcea, and Lessonia, and in all parts alike the 

 larger mass of seaweed belongs to Melanosperms, though 

 the Rhodosperms and Chlorosperms may number more 

 species. 



* Thuret, 1. c. vol. 14, tab. 31 ; vol. 16, tab. 1. 



