396 
this work, by stating the opinions of those who have given the greatest atten- 
tion to particular tribes, rather than by offering any thing novel myself. I 
trust, however, I may, without incurring the charge of presumption from 
those great cryptogamists whose lives have been devoted to the study of the 
subject, offer here and there a few remarks upon the analogy that exists 
between the more anomalous forms of Acrogens and those of Flowering 
Plants : I venture to do this with the more confidence, because the truth of 
any opinions I may advance will have to be tried by the general laws of 
vegetable organisation, and upon principles which do not depend upon an 
extensive acquaintance with species. 
There has not been any very satisfactory arrangement of the orders of 
Acrogens. De Candolle refers Ferns and their immediate allies to Endogenous 
plants, and separates the remainder of Acrogens mto FoUacea, or plants with leafy 
expansions, and Aphyllce, or those destitute of leaves : but to the first of 
these there are grave objections ; the second nearly corresponds with the 
arrangement here adopted. 
Agardh, in 18*21, divided them thus : — AcoxYLEDONEiE, or leafless jDlants, 
with all the parts confluent, the colour not herbaceous, with no sexes, and 
propagated by sporidia. (Sporidium est corculum nudum, radicula, cotyle- 
done et hilo destitutum. Aph. 71.) Pseudocotyledone^, or leafy plants, 
the parts of which are sometimes confluent, the colour green, with an attempt 
at producing sexes, and propagated by sporules enclosed in capsules. (Spora 
est corculum perispermio (?) et membrana simplici hilo destituta inclusum, 
germinatione cotyledonidium (analogon cotyledon! folium) explicans. Ihid. 
71,) To Acotyledoneee he refers only Fungi, Lichens, and Algae, and com- 
prehends the remainder in Pseudocotyledoneae. This arrangement is undoubt- 
edly natural, but it is liable to objection, on the ground, that although the 
two groups are distinct, yet it is extremely uncertain whether the characters 
assigned to each are founded upon accurate observation. For instance, the 
distinction drawn between their modes of reproduction or germination is 
altogether arbitrary. It is well known that Mosses and Confervas are so 
similar when germinating, that young plants of the former have been de- 
scribed as belonging to the latter tribe (see Dmmmond’s paper in the Trans- 
actions of the Linnean Society ^ 15. p. 20.) ; and yet one is said to increase by 
sporules, and the other by sporidia. The confluence of all the parts in Acoty- 
ledoneae, and the separation of them in Pseudocotyledoneae, will not distin- 
guish them ; witness Marchantia, Riccia, &c. in the latter, and such species 
as Caulerpa hypnoides in the former. Colour is a stiU less satisfactory differ- 
ence : for example, what green have we in Mosses or Ferns, or other Pseudo- 
cotyledonese, more intense than in Ulva and numerous Algae among Acotyle- 
doneae ? As to a supposed tendency to developement of sexes in one and not 
in the other, this may possibly be the case ; but it is no character of the two 
groups ; for what better proof have we of any such tendency existing in 
Lycopodiaceae or Hepaticae, than in Lichens. 
Fries, in his Flantce Homonemea, adopts these divisions, but assigns them 
new names and characters. He calls the Acotyledoneae of Agardh Homo- 
nemea, and Pseudocotyledoneae he terms Heteronemea, with the following 
characters : — Heteronemea. Germinating filaments, combining in a hetero- 
geneous body. Some analogy to the difference of sexes. Tissue consist- 
ing of cellules regularly united. Homonemea. Germinating filaments, 
either distinct or combining in a homogeneous body. No trace of sexual 
differences. Tissue consisting of anomalous, somewhat filamentous cellules. 
— I scarcely know whether to consider these definitions more satisfactory 
than those of Agardh ; perhaps they are : but their fault is evidently that 
