ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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which are described in detail, in the constitution of the vascular cylinder 
and in the presence of special formations in the cortex. Another 
peculiarity consists in the presence at the base of the branch of formations, 
consisting of phloem only, or of both xylem and phloem, originating 
from the endoderm. 
Conducting Cells in Gymnosperms.* — Prof. E. Strasburger de- 
scribes the nature of the cells which, in Gymnosperms, perform the 
function of the conducting cells in the sieve-portion of the vascular 
bundles of Angiosperms. In Vascular Cryptogams this function is 
performed by elongated parenchymatous cells containing more or less 
protoplasm, which either surround the sieve-tubes or are intercalated 
between them. In Gymnosperms also similar elements are found ; there 
is always a relationship between the sieve-tubes and certain parenchy- 
matous elements which surround them. In the Abietinem this function 
is performed by certain rows of cells in the medullary rays ; in a portion 
of the Cupressinese aud Taxodineae, by certain rows in the medullary 
rays, and by others in the bast-parenchyme ; in another portion of the 
Cupressineae and Taxodineae, and in the Taxineae and Araucarieae, by 
rows in the bast-parenchyme only. The arrangement in the Gnetaceae 
and Cycadeae resembles most nearly that in the Araucarieae. The pecu- 
liarities of structure in the different suborders is described in detail ; 
the parenchymatous cells which have this relation to the sieve-tubes all 
agree in being comparatively rich in protoplasm ; in containing, when 
they are most active, no starch, and in the fact that they finally 
communicate with the sieve-tubes by pits of a peculiar kind. 
Assimilating Tissue in Atriplex nummularia.f — According to 
Prof. G. Arcangeli, in the leaves of this shrubby species of Atriplex, the 
epiderm is alike on both sides, and the palisade-tissue is transformed 
into an assimilating tissue consisting of cells nearly destitute of chloro- 
phyll, but containing abundance of water ; and the sheath of the vascular 
bundles has undergone a similar transformation, this being apparently 
the chief seat of the assimilating function. A similar structure occurs 
also in the wings of the leaf-stalk ; and it is probable that it is presented 
also by other species of the genus which grow in dry sunny situations. 
Mucilage-cells in the Seeds of Cruciferse.j: — M. J. D’Arbaumont 
states that it is well known that many families, and notably Crucifeise, 
contain, in their peripheral and epidermal cells, a mucilaginous sub- 
stance which has the property of considerably swelling in water. 
Several opinions have been put forward as to the nature and anatomical 
value of mucilage-cells. According to several authors, their walls 
remain thin, and the mucilaginous substance accumulates as a deposit 
in their cavity, and ends by filling it up entirely. According to others, 
the mucilage forms solely in the external walls of the cells, which conse- 
quently thicken considerably. 
The author commences with a careful study of the seeds of Gapsella. 
When the seed has arrived at maturity, the epidermal cells lose some of 
their water ; they contract and flatten, and take that consistence which 
* SB. K. Preuss. Akad. Wiss., 1890, pp. 205-16 (1 pi.). 
t Nuov. Giorn. Bot. Ital., xxii. (1890) pp. 426-30. 
X Ann. Sci. Nat. (Bot.), xi. (1890) pp 124-84 (1 pi.). 
