396 Miscellaneous. 
forms the dissepiment. Like the latter they admit neither fibres nor 
vessels ; and in this respect their parallelism with the placentas can 
no longer be traced—just as, moreover, we cannot compare the pollen 
lying free in the cells, like the spores in the capsules of mosses, with 
ovules attached to placentas. 
In the placentoids we have never observed the so-called fibrous 
cells which form a part of many dissepiments ; it would appear, there- 
fore, that the presence of placentoids, always of a parenchymatous 
nature, is connected with that of dissepiments of the same histolo- 
gical nature. 
The placentoids, like the dissepiments, are usually covered by a 
fold of the nutritive membrane or third membrance of the anther. 
3. Biology of the placentoids.—The function of the placentoids 
appears to be to assist in the formation of the pollen. They originate 
about the same period as the latter, follow it in their development, 
and disappear when, as its maturation approaches, they become use- 
less to it, their persistence being even capable of hindering its disse- 
mination. 
The essentially parenchymatous structure of the placentoids, and 
the nutritive membrane which clothes them, and of which they thus 
serve to multiply the surfaces or points of contact with the pollen, 
are evidently conditions appropriate to the part which we ascribe to 
the new organ. We are, moreover, the more struck with the utility 
of an organization which has the effect of bringing nutriment every- 
where within reach of the body to be nourished, as the latter (the 
pollen) does not, like the ovules, receive its nourishment by conti- 
nuity, but indirectly and by simple contiguity. , 
4. The placentoids in their relation to taronomy.—When a new 
organ is discovered in plants, it becomes necessary for the history of 
this organ to inquire what relations of existence it may possess with 
the natural divisions of the vegetable kingdom. ‘This first point 
being determined, it will become possible to appreciate the significa- 
tion of the existence of placentoids in its relations with the various 
degrees of organic elevation of species of plants. 
Placentoids exist in no monocotyledonous plant. Among the 
Dicotyledons, the Dialypetalee (Monochlamydez and Thalami- 
florze) are also destitute of placentoids. The same might be said of the 
Calyciflorze if we had not observed these organs in Cassia marilan- 
dica. There remain the Corolliflore ; and it is in a certam number 
of families of this class that we have found the anthers to be habitu- 
ally provided with placentoids, which exist 
In the Gentianacee (Chlora, Chironia) ; 
In the Solanacee (Atropa, Habrotamus, Hyoscyamus, Lycopersi- 
con, Solanum, Witheringia) ; 
In the Scrophulariacee (Hemitomus, Pedicularis, Verbascum ; 
not in Veronica and Chelone) ; 
In the Labiate (Salvia, Rosmarinus, and Westringia, genera 
with unilocular anthers; and Lamium, Leonurus, and Marrubium 
with perfect anthers) ; 
In the Acanthacee (Acanthus, Justicia, &e.) ; 
