354 Linnean Society. 
one species (HL. Wallichianum) approaches in density-to woody fibre. 
The parenchyma within the tubes is disposed with less regularity 
than in the leaves and sheaths, and their outer green parietes abound 
with stomata. With one exception, the number of tubes in the 
sheaths bears an exact relation to that in the peduncles of two to one. 
The author describes the cavities existing in some Alismacee, Pon- 
tederie, Cyperacee and Nelumbinee, as originating in the same man- 
ner as the chambers in the tubes of Hriocaulon, from the interposi- 
tion of cellular septa perforated by fissures caused by the separation 
of the cells and not by any interruption of the membrane. In Pon- 
tederia dilatata raphides are found in great abundance in cells at- 
tached to the septa in such a manner as to project at right angles 
beyond either surface, and to occupy the spaces left by the separa- 
tion of the ordinary cells. The same disposition occurs in some 
Aroidee. | 
The existence of stomata in the submerged leaves of H. setaceum 
is mentioned as rather corroborating than weakening the general 
rule laid down by M. Adolphe Brongniart, that submerged leaves are 
destitute of cuticle. The stomata of Hriocaulonee are described at 
length, and regarded as offering excellent examples of the correct- 
ness of M. Brongniart’s statements with regard to the nature of these 
bodies. Their aperture communicates directly with the interior of 
the leaves, and is invariably occupied by air; the communication in 
E. setaceum, and in two other species in which the parenchyma is 
confined to the upper surface, being uninterrupted; while in the 
leaves of those species in which the parenchyma is deposited on the 
lower as well as the upper cuticle, there is invariably an open space 
left in it, corresponding with each stoma, and this opening appears 
always to be occupied by a bubble of air. The author states, how- 
ever, that he is far from considering it proved, that such a free com- 
- munication through the stomata, although the same structure is ob- 
vious in other plants belonging to different families, is universally 
present. 
As Xyridee present none of the peculiarities of organization above 
mentioned, Mr. Griffith considers these peculiarities as corroborative 
of the correctness of Richard’s opinion, since adopted by Professor 
Von Martius, that Hriocaulon is the type of a distinct family. 
December 16.—E. Forster, Esq., V.P., in the Chair. 
Read a memoir “‘ On the causes of disjunctions of Vegetable Sub- 
stance, especially those which are horizontal.” By the Rev. William 
Hincks, F.L.S. &c. &c. 
After some preliminary observations on the subject of disruptions 
in general, the author briefly notices certain cases of vertical disrup- 
tion, and then proceeds to the more immediate object of his paper, 
the horizontal separation of vegetable substance by natural means. 
This, he observes, may take place in the axis itself, or in any of the 
organs connected with it at their points of attachment, as in the fall 
of the leaf, of sepals and petals, of entire flowers and fruits, and in 
the separation of such buds as form caulinary bulbs ; or it may occur 
