126 DECAISNE AND THURET. [BOOK i. 



The nature of these minute organs deserves more attention 

 than it has obtained, for they are produced with too much 

 regularity to be regarded as accidental. On P. fastigiata 

 they are so abundant as to give the frond a yellow colour 

 to the naked eye." 



In this description Dr. Harvey, like myself, rejects the 

 hypothesis that sexes occur among Algals. A totally different 

 view has been taken by MM. Decaisne and Thuret, whose 

 account of what they imagine to be sexes I extract at length 

 from the Annales des Sciences, vol. iii. of the third series. 



" The conceptacles of FucaceaB are bisexual or unisexual. 

 The first contain both spores and antheridia, and in this case 

 the plant is said to be hermaphrodite (Ex. Fucus canalicu- 

 latus, tuberculatus, Halidrys siliquosa). The latter contain 

 neither of these organs, and two cases may then be distin- 

 guished : sometimes (as may be occasionally seen in Fucus 

 nodosus) two sorts of receptacles are found on the same stem, 

 the one bearing male and the other female conceptacles : the 

 plant is then moncecious. At other times the same stem 

 bears but one and the same sort of conceptacle, (as in Fucus 

 serratus, vesiculosus), in which case the plant is dioecious. 

 These definitions appeared to us to require explanation ; but 

 they are far from being accurate ; for as we descend the scale 

 of vegetation, organisation becomes more and more simple, 

 the inflorescence is confounded with the flower, and the 

 terms used to express the organisation of comparatively per- 

 fect plants cannot be applied with precision to plants which 

 are much less developed, 



"As examples of dioecious Fuci, we may give F. serratus 

 and F. vesiculosus. It is, indeed, not uncommon to find her- 

 maphrodite conceptacles in individuals allied to the latter 

 species ; but it must be remembered that under the name of 

 F. vesiculosus many species are confounded, which were for- 

 merly distinguished, and which must again be admitted as so 

 many different types, and not, as at present, as mere varieties 

 of one and the same thing. It is, however, very easy to dis- 

 tinguish the male receptacles in unisexual Fuci by the orange 

 tint of their antheridia. The latter consist of ovoid vesi- 

 cles containing a white substance scattered over with red 



