64 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
are only partially applicable to the fifty species of Potamogeton or to 
the other freshwater genera. The generic characters derived from the 
anatomy of the leaf do not always correspond to those founded on the 
structure of the flower. Contrary to the general opinion, the epiderm is 
not the sole seat of the chlorophyll in the marine species ; it is found 
also in the cells of the parenchyme, but generally only in small quantities. 
Cells containing tannin occur in several genera both in the epiderm and 
in the parenchyme. 
None of the marine species examined contain stomates ; and this is 
also the case with the greater number of the freshwater species ; but in 
some species they occur constantly or nearly so. 
In the genera Zostera, Phyllospadix , Halodule, and some species of 
Potamogeton , the leaves have an apical opening at the termination of the 
median vein. This opening is formed at an early period by the dis- 
appearance of certain epidermal cells. Its purpose appears to be to 
place the plant in communication with the surrounding medium, and 
thus facilitate the exchange of liquid between the plant and the medium. 
Aquatic plants are permeated by currents of water comparable to the 
transpiration-current in land-plants ; and, when deprived of their roots, 
they continue to flourish by absorbing water through their leaves. 
Pitchers on a Cabbage-leaf.* * * § — M. W. Russell describes several 
examples of ascidiform structures on cabbage-leaves. The first instance 
is of a funnel-shaped pitcher which may be compared to a leaf with a 
long stalk which has been rolled on itself, the margins having become 
more or less completely united. In the remaining examples we have a 
pitcher-like structure springing from the upper surface of the leaf. 
From the arrangement of the vascular bundles the author regards these 
epiphyllous pitchers as examples of the doubling of a normal leaf. 
Leaves of Fossil Banksias.f — Freih. v. Ettingshausen describes a 
number of remains of leaves from the Tertiary strata of Switzerland, 
which he refers to the existing Australian genus of Proteacese, Banksia, 
including also in the same genus those described by Heer under the 
name Bryandroides. He concludes that the fossil resembled the existing 
species of the genus in being polymorphic. 
Aerial Roots of Vitis vulpina.J — Mr. T. Meehan describes the 
perennial aerial roots of this vine, which he suggests are a survival of an 
earlier creeping habit by means of rhizome-like stems before it acquired 
the habit of climbing by tendrils. 
/3. Physiology. 
(1) Reproduction and Embryology. 
Morphology of the Phenomenon of Impregnation^ — M. L. Gui- 
gnard discusses the part played by the “ directing spheres ” (tinoleucites) 
in the process of impregnation, and concludes, from the facts observed 
in Lilium Martagon and Fritillaria, that the process consists not merely 
in the coalescence of two nuclei of different sexual origin, but also in the 
* Rev. Ge'n. He Bot. (Bonnier), iii. (1891) pp. 33-42, 337-40 (7 figs.). 
t SB. Akad. Wiss. Wien, cxix. (1890) pp. 475-90 (2 pis.). 
j Proc. Acad. Nat. Sci. Philadelphia, 1891, pp 275-6. 
§ Comptes Rendus, cxii. (1891) pp. 1320-2. Cf. this Journal, 1891, p. 614. 
