with descriptions of new genera and species. 165 



The conjugation of the Diatomacea seems to throw some light 

 upon a question of much interest with respect to the real nature 

 of certain vegetable structures, respecting which many eminent 

 botanists are at present at issue. The structures alluded to are 

 the so-called untheridia and pistillidia (archegonia) of Mosses. 

 The paper on this subject by Mr. Valentine* would seem to 

 settle the point that there can be no impregnation of the con- 

 tents of the moss-capsule by the introduction into its cavity 

 of any external substance, after the formation of the sporules. 

 On the other hand, the learned authors of the ' Bryologia Euro- 

 paea ' state with emphasis that certain species of Mosses, which 

 are dioicous, — that is, some plants of the same species bearing 

 antheridia only, and others only archegonia, — do not bear fruit 

 unless the male plants (those with antheridia) are in the neigh- 

 bourhood of the plants possessing archegonia. It is perhaps not 

 impossible to reconcile these at first sight apparently conflicting 

 opinions. It may be that impregnation takes place before the 

 production of the capsule ; — that the cell from which the capsule, 

 with its seta, &c. is developed corresponds with the sporangium 

 of the Diatomaceous plant or the embryonic cell of the flowering 

 plant ; that this cell contains a mixed endochrome derived partly 

 from the antheridia ; and that the entire capsule (with its con- 

 tents, appendages, &c.), the further development of this primor- 

 dial cell, corresponds to a perfect seed of the flowering plant, or 

 to the aggregate of the sporangial frustules of a Diatomaceous 

 plant. It is true that in some of the Mosses the structure of the 

 capsule appears very complicated, but it is upon a very simple 

 type, as shown in other species : and, moreover, the sporangial 

 frustules of the Diatomaceous plant possess cell-walls as highly 

 developed as occurs in any other phase of the species. In some 

 of the Conjugates there is also a division of the reproductive 

 mass before this escapes from the plant, so that the numerous 

 sporules of the Moss furnish no argument against the hypo- 

 thesis just advanced. As a further argument in favour of the 

 "lea of the capsule of the Moss being the product of a mixed 



Idochrome, it is stated by Bruch and Schimper that the cap- 

 e itself is not developed unless the two so-called sexes of the 

 eies are in proximity. 



There now remains to consider a tribe of the Diatomacea, 

 namely the Meloseirece, which would at first seem to offer an 

 exception to the usual mode of reproduction in this family, but 

 the exception is probably rather apparent than real. In those 

 ecies of Meloseira and its allied genera which have been met 



ith in fruit, there is no evident conjugation or mixture of endo- 



* Linn. Trans, vol. xvii. p. 465-481. 



