498 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
(3) Structure of Tissues. 
Function of the Protecting-sheath.* * * § — From experiments made with 
different species of snails, Herr A. Dreyer concludes that the tannin 
contained in the protecting sheath is an efficient protection against con- 
sumption by these animals. The odoriferous oil in the root-stock of the 
onion answers the same purpose ; and the same is the case with the 
alkaloids of Aconitum Napellus, Veratrum album , Colchicum autumnale, 
and Cicuta virosa. The function of the protecting-sheath is not, there- 
fore, a purely mechanical one ; it serves also a conducting purpose. It 
does not, however, appear to afford any protection against the attacks of 
parasitic fungi or bacteria. 
Sieve-tubes in the Xylem.j — Pursuing his researches on this subject, 
Prof. E. Chodat records the occurrence, in a large number of natural 
orders, of islands of sieve-tubes produced from a cambium which acts in 
a centrifugal direction, forming sometimes xylem, sometimes a soft tissue 
with sieve-tubes. In other orders an adventitious xylem is formed from 
a supernumerary generative layer produced at the expense of the peri- 
cycle. 
Structure of Phytolacca.ij: — Dr. 0. Krueh describes several details 
in the anatomical and histological structure of Phytolacca dioica. The 
chief structural specialities are the presence of vascular bundles in 
the pith, and the increase in thickness of the branches by the formation 
of supernumerary rings. On the principal axis each leaf has, as a rule, 
two buds in its axil, of which the one nearest the axis usually developes 
into a branch, while the other remains undeveloped. On the flowering 
branches, on the other hand, the axil of each leaf bears only a single 
bud. 
C4) Structure of Organs. 
Pollen-grains of Papaveraceae.§ — Dr. E. Baroni describes the 
pollen-grains of the following species of Papaveracese : — Papaver 
orientale , setigerum, and somniferum , Chelidonium majus, and Eschscholtzia 
crocea. The measurements are given of the dry grains, and the changes 
are described which are produced by immersion in water, solution of 
sugar, and glycerin. 
Development of the Integument of the Seed. — M. L. Guignard || 
describes the development of the integument of the mature seed in the 
Cruciferse and in some other orders, his conclusions differing in several 
points from those of Brandza.1I 
In the Cruciferee the observations were made on a large number of 
species belonging to all the more important tribes. In all cases he 
finds that the internal proteinaceous layer of the testa is derived from 
the outermost layer of the endosperm, the aleurone layer of authors, and 
* ‘ Beitr. z. Kermtniss d. Function d. Schutzscheide,’ St. Gallen, 1892, 57 pp. 
See Bot. Centralbl., liii. (1893) p. 383. 
t Arch. Sci. Phys. et Nat., xxviii. (1892) pp. 481-2. Cf. this Journal, 1892, 
p. 500. t Atti R. Accad. Lincei, ii. (1893) pp. 52-5. 
§ Nnov. Giorn. Bot. Ital., xxv. (1893) pp. 130-5. 
|| Journ. de Bot. (Morot), vii. (1893) pp. 1-14, 21-34, 57-66, 97-106, 141-53 
(80 figs.); and Bull. Soc. Bot. France, xxxix. (1893) pp. 392-4; xl. (1893) pp. 56-9. 
«f Cf. this Journal, 1891, p. 491. 
