68 MB. R. J. HARVEY GIBSON ON THE STRUCTURE 



On the Structure and Development of the Oystocaifcs of Gate- 



nella Opuntia, Grev. By E. J. Hvrvet Gi#30N, M.A., 

 F.L.S., F.E.S.E., Lecturer on Botany in University College, 



Liverpool. 



[Bead 18th December, 1890.] 

 (Plates XIII. & XIV.) 



The classification of Alga) is a subject on which systematica 

 are very far from being unanimous ; and this is especially due to 

 the fact that we are ignorant in very many cases of the structure 

 of the reproductive organs of type forms, chiefly among the 

 Rhodophyceae. 



The alga, the structure of whose fruits forms the subject of 

 the present paper, common as it is on our shores, is a striking 

 example of the difficulty of classifying a member of the group 

 Floridese on vegetative characters alone. As long ago as 1830 

 Greville * wrote : — "-The peculiarity of the internal structure or 

 this alga has induced me to separate it from all others, even m 

 the absence of fructification, and, in conjunction with its habit, 

 to place it amongst the Gtastkocarpe^. It has ever been con- 

 sidered in the light of a doubtful plant, and has successively held 

 the title of Ulva, Fucus, Hivularia, Gigartina, Chondria, Haly- 

 menia^ Lomentaria, and, lastly, mirabile dictu, of Chordaria in 

 Sprengel's ' Systema Vegetabilium ' ! I have endeavoured — not, 

 I think, without sufficient cause — to afford this almost universal 

 trespasser something more like a ' local habitation and a name.' " 



The cystocarps of Catenella Opuntia have hitherto remained 

 almost an unknown quantity. Groodenough and Woodward t, 

 after describing the articulations as oval, say " quorum supremi 

 tuberculorum officio funguntur, et seminibus minutissimis con- 

 gests foeti sunt." It is difficult to say from this description 

 and from their figures whether these modified articulations were 

 tetrasporic or cystocarpic, although in all probability they were 

 the former. 



Greville % affirms that the fructification was unknown in his 

 day ; but he adds that Lightf oot believed that the joints of the 

 frond were the situations where " minute seeds " were to be 



* 'Alg» Britannicse,' p. 166. 



t Trans. Linn. Soc. vol. iii. p. 219. 



{ hoc. cit. p. 1()7. 



