100 DEVELOPMENT OF THE FLOWER. 
much smaller than the true ones, subsequently they all assume 
nearly the same size. 
The existence of sinuses in all simple stigmata is irrecon- 
cilable with the hypothesis of the stigma being the apex 
of the midrib, whereas it is easily explainable by the hypo- 
thesis of the stigma being derived from margins of the car- 
pellary leaf. 
In a true normal simple stigma, the sinuses will be two ; one 
will exist at the point where the stigmatic surface passes 
into the stigmatic canal, another opposite the termination 
of the midrib of the carpellary leaf. The existence of a 
mucro in this direction, shewing the point of the leaf, is 
subversive of the same hypothesis. 
Among theoretical objections to this, I might mention 
that if the stigma be the apex of the midrib, it can in no 
case form a direct communication with the stigmatie canal, 
which is nothing more than the space between the cohering 
margins of the leaf, and its dorsal vein. And in all cases 
of penetration of the pollen tubes passed down in the direc- 
tion of the origin of the stigma, they would meet with the 
hardest, instead of the softest tissue of the structure. This 
however, would be a theoretical, rather than a practical 
objection, since there are reasons for supposing that in 
some cases no actual penetration takes place, the tubes after 
having been excited by the stigmatic tissue, passing down 
directly into the stigmatic canal, as in Thunbergia, Viola, etc. 
in which the end of the stigmatic canal is plainly open. 
—. In Dr. Lindley's prefatory remarks to the Illustration* 
of Orchidez, it is positively allowed, from the consideration 
of Orobanchez, that placentz may arise as well from the 
axes as from the margins of carpels. 
Lindley says that the analogies to coste of Orchideous 
carpels may be regarded as the united margins of the carpels, 
or as imperfect carpels, attributing therefore axile placente 
to this family. 
Mr. Brown's explanation of the structure of that family 
is partly attributed to his supposing “in common with all 
* Genera and species of Orchid. 
