TRANSACTIONS OF THE SECTIONS. 97 
and contained a description of the varieties of vegetation within a district of about 
2,000,000 square miles, extending from the Gulf of Mexico to the northern bounda-~ 
ries of Canada, and from the Atlantic Ocean to the western prairies. 
Note on certain Influences regulating the Forms of Leaves, gc. 
By Maxwett T, Masters, M.D., F.L.S. 
The object of this communication was, lstly, to show the cause of the groove 
so generally met with on the upper surface of the leaf-stalk ; and, 2ndly, to account 
for the oblique form of certain leaves. 
With reference to the furrow on the leaf-stalk, it was shown that this is a provi- 
sion to prevent undue pressure on the young growing leaf-bud, and at the same 
time to economize space. The truth of this notion is borne out by an examination 
of the leaf-bud, as well as by the fact that when, from various causes, no pressure 
is exerted, the leaf-stalk is not grooved, but cylindrical. A similar explanation 
may be given of the inner palea of grasses, which presents a central groove, into 
which the axis of the spikelet is received, and which is bounded by the two pro- 
minent ribs always present in that organ. In many Restiacee a similar provision 
exists against eatlae pressure: whenever, in these plants, a bract or scale 1s closely 
pressed up against the stem, that scale is provided with lateral ribs, bounding a 
central furrow, as in the upper palea of grasses; this scale, moreover, is frequently 
provided with a coating of hair, which affords additional protection against pres- 
sure. In other species, where no pressure is exerted, the scale is either entirely 
absent, or, if present, destitute of the lateral ribs and intermediate furrow. Similar 
illustrations may be found in the bracts of Iris, Philydrum, Gladiolus, and very 
many other plants. The obliquity of leaves was shown to be, in many instances, 
the result of a process of mutual accommodation, whereby one portion of a leaf is 
restricted in its growth by the nearness of a neighbouring leaf, while another part 
not so cramped for space grows to a proportionately greater extent—a process 
precisely resembling that which takes place in the outermost florets of some Cru- 
cifers, e.g. Iberis, the outer petals of some Umbellifers, &c. In the lime, the 
hazel, the mulberry, and many other plants, the leaves are oblique at the base, and 
‘the branch is bent away from the les f at a considerable angle—is, in botanical lan- 
guage, flexuose; a space is thus left, which is filled up by the larger segment of 
the base of the leaf. Now, if a line-be drawn across a lime leaf in such a direction 
as to cut off the projecting lobe at the base, it will be seen that this line is nearly 
- parallel in direction to that part of the stem above the leaf in question, and from 
which it is deflected. The direction of this line is usually the same as that of the 
first or second lateral vein proceeding from the midrib towards the margin of the 
leaf, counting from the base of the leaf upwards. Several instances from natural 
as well as from exceptional leayes were adduced in support of the opinion just 
expressed; at the same time it was admitted that this explanation did not sutfice 
to account for all cases of the kind, that of Begonia among others, 
ZooLoey. 
Descriptions of New British Polyzoa, with Remarks on some imperfectly 
known Species. By JosHua ALDER. 
The species forming the subject of this communication belong chiefly to the 
MAcishied. calcareous forms of the genera Cellepora and Eschara. The new species 
described were named Cellepora levigata, Eschara ligulata, and Palnucellaria elegans, 
the latter also a new genus, which is characterized as follows :—Polyzoary erect, 
calcareous, inarticulate, cylindrical, smooth, branching dichotomously. Cells dis- 
posed in four longitudinal, alternate series, those on the two opposite series being 
on the same level. Apertures circular, with a broad, projecting, palmate expansion 
in front, bearing an avicularium. This genus is proposed for a beautiful little coral 
dredged this year in Shetland by the Rev. A. M. Norman. The species remarked 
upon included the Eschara levis of Fleming, a species lost sight of by British natu- 
sate - many years ; Eschara Landsborovit, now first ascertained to be an Eschara, 
: it 
