SCIENTIFIC SUMMARY. 
491 
by M. A. Trecul. The roots have in the first instance the normal character,, 
but after a while they undergo a series of modifications which give two dif- 
ferent structures, corresponding to two periods of development. The different 
layers are as follow : — 1st period (1), the outer bark, (2) a generative layer,. 
(3) a vascular zone, (4) a cortical layer, and (5) a vascular axis. In the second! 
stage there are : — (1) Outer bark, (2) ordinary generative layer, (3) a vascular- 
zone with a normal direction of its bundles, (4) a generative layer, (5) a cortex 
layer with proper vessels, (6) a zone of vascular bundles also directed in the 
usual manner, (7) a zone of inverted vascular bundles, (8) a generative layer- 
(9) a cork layer, (10) a vascular bundle. 
Wolffia Arrhiza in England. — Dr. Henry Trimen has discovered this plant 
in a pond near Staines, Middlesex, as recorded in our last. Dr. Trimen', in a 
paper published on his discovery, remarks that a good description of the plant 
is to be found in Hoffmann’s paper in “ Weigemann’s Archives.” In no figure-, 
however, is shown satisfactorily the oblique way in which the new frond 
springs from its parent ; nor, according to Dr. Trimen, does any plate express- 
clearly the peculiar sort of convexity of the upper surface of the frond. This 
convexity is from side to side, the upper surface seeming, as it were, to over- 
lap the sides of the frond, so that it is only by the want of the stomata, and 
the lighter colour, that it can be seen where the upper surface ceases. 
The Phylloid Shoots of Sciadopitys. — In certain plants when the leaves 
become reduced in size, the young shoots take on part of the functions of 
the foliar organs, and expand into leaf-like growths. This peculiarity in the 
above-named plant has been well and carefully described by Dr. Alexander 
Dickson, who states that in Sciadopitys the leaves of the growing shoots are 
really leaf-scales. In each year’s growth the lower scales are placed at some 
distance from each other, and for the most part do not produce axillar 
branches. The scales toward the extremity of the year’s growth, on the other 
hand, are closely approximated to each other, and in their axils are produced 
those bodies which have hitherto been termed the leaves of the plant. They 
are green linear organs, bearing a considerable resemblance to the leaves of 
other conifers, and occur singly in the axils of the scales. They are slightly 
bifid at their extremity, and exhibit a pretty deep mesial furrow on both 
upper and under surface. Dissection shows two vascular bundles, one on 
either side of the mesial line, in which respect they differ essentially from 
those scales which in young specimens of this plant are occasionally developed 
as elongated green leaves, and which invariably exhibit a middle vascular 
bundle. It follows, therefore, that the phylloid organs in Sciadopitys differ 
from true leaves not only in position but in structure. — Vide The Journal of 
Botany, July. 
Plants in Egyptian Bricks. — Some curious discoveries have been made by 
Professor Unger, who has been examining certain bricks from the Pyramid of 
Dashour (3400 B.C.). The bricks, which must have been made of the Nile 
mud or slime of the period, have been found to contain many vegetable and 
animal remains. By this discovery Professor Unger makes us acquainted 
with wild and cultivated plants which were growing in the pyramid-building 
days ; with freshwater shells, fishes, remains of insects, and so forth, and a 
swarm of organic bodies, which, for the most part, are represented without 
alteration in Egypt at the present time. Besides two sorts of grain — wheat 
YOL. Y. — NO. XXI. 2 L 
