PREFACE. 



Although this work has greatly exceeded the limits which 

 I originally contemplated, I am very far from thinking that 

 it has exhausted the subject. About one-third of the Des- 

 midiese which it describes have been discovered in this 

 country since the prospectus was issued ; a fact which may 

 well warrant the expectation that a rich harvest yet remains 

 to reward the diligence of future labourers. In regard also 

 to the reproductive organs ; whilst I have the pleasure of 

 noticing that the sporangia of fifty species are here figured, 

 most of them for the first time, I would point out that those 

 of a much larger number are still unknown, and that every 

 spring and summer many are brought to light. 



In compliance with the request of some of my Subscribers, 

 I have added a few foreign habitats, which will give some 

 idea of the geographical distribution of the species. This I 

 am enabled to do through the kindness of M. de Brebisson 

 and Professor Bailey, who have furnished me with complete 

 lists of the species found by them. It must of course be 

 considered merely the first rude chart of their range, and I 

 earnestly deprecate any comparison of it with what Professor 

 Harvey has accomplished for the Marine Algce in his splen- 

 did ' Phycologia Britannica': nevertheless enough is here 

 exhibited to show the cosmopolite character of these plants, 

 since not only has almost every British species been found at 



