i abe ge oi ai i al all 
— eene meme 
PREFACE. xxvii 
nute granular matter, they contain a structure totally 
irreconcileable with the idea of their being gemma. 
The remains of these sacs may be always found in the 
cavities in which they are formed, and from which 
they cannot escape. This is the more remarkable as 
in Riccia the fruit always becomes exserted. I look 
upon the existence of the elaters as similar with that 
of fibrous cells of the endothecum ; and I attach con- 
sequently very little importance to their existence, 
The direction of growth consequent on fecundation 
is directly opposite to that of mosses, Marchantia and 
Targionia are remarkable for their stomata. "The ex- 
istence of which evidently depends upon their being 
furnished with a cuticle. This in Riccia is exceeding- 
ly rudimentary. 
Characee.—Much light has been lately thrown on 
these obscure plants, particularly as regards their cir- 
culation by Varley, Solly and Slack. 
The nucule is really monospermous. 
REMARKS ON OvuLa 
An ovulum is, at its earliest period of existence an 
extension from some part of the surface of the pla- 
centa, it is at this time rounded sessile, entirely cellular, 
and without the slightest trace of any integuments. 
The first change that takes place is its separation to a 
greater or less extent from the placenta by the elonga- 
tion of portion of this last, forming the funiculus, the 
next change is the marking out of its subsequent coat 
or coats by one or generally two lines of construction, 
the uppermost of which is however first formed, 
when two of these lines are formed, the ovulum is di- 
