165 
with descriptions of new genera and species. 
The conjugation of Diatomacece 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 antheridia 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- 
psea ^ 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 
idea of the capsule of the Moss being the product of a mixed 
endochrome, it is stated by Bruch and Schimper that the cap- 
sule itself is not developed unless the two so-called sexes of the 
species are in proximity. 
There now remains to consider a tribe of the Diatomaces, 
namely the Meloseires, 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 
species of Meloseira and its allied genera which have been met 
with in fruit, there is no evident conjugation or mixture of endo- 
Liiiii. Trans, vol. xvii. p.46o-lS4. 
