500 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Secondary Xylem of the Apetalse.* — M. C. Houlbert has undertaken 
an examination of the structure of the secondary wood in the orders of 
Apetalae with inferior ovary, for the purpose of determining its value in 
connection with classification. 
The Proteaceae may be classified from this point of view in three 
groups : — (1) In the Banksia group the vessels are arranged in concen- 
tric zones ; (2) in the Ozites group they form incomplete arcs terminated 
by wings of woody parenchyme ; (3) in the Protea group the vessels are 
dispersed irregularly through the woody fibres. In Myrica (Myricaceae) 
the general structure is absolutely the same as in Persoonia. The 
secondary xylem of the Piperaceae is composed of woody fibres in radial 
bands, among which the vessels are arranged in simple rows or in 
clusters ; a similar structure occurs in the Chloranthaceae and the 
Garryaceae. In the Chenopodiaceae the structure of the secondary xylem 
is subject to considerable variation. The Thymelaceae are characterized 
by the small number of vessels ; the arrangement of these justifies the 
division of the order into the two groups generally adopted, the Aquilarieas 
and the Thymeleae. In the Polygonaceae the structure of the secondary 
xylem is very uniform, the vessels are large and isolated, and are rarely 
accompanied by woody parenchyme. The Urticaceae probably comprise 
plants of very various origin ; two types may be distinguished, (1) the 
Urticoideae characterized by broad transverse bands of woody paren- 
chyme at the level of the vessels ; (2) the Ulmo'ideae in which the woody 
parenchyme is wanting, or but slightly developed. 
Stem of Phaseolus Caracalla.j — Prof. A. Borzi describes an ano- 
maly in the structure of the stem of this plant. It consists chiefly in 
the unlimited production of phloem-bundles of a tertiary character, 
which insert themselves between the elements of the secondary xylem. 
Other Leguminosae — Abrus precatorius , Wistaria chinensis , Bhynchosia 
phaseoloides , Pueraria Thunbergiana , the species of Bauhinia of the 
section Caulotretus — present the anomaly of the production of tissues of 
a tertiary character from the activity of one or more supernumerary 
generating zones. The peculiarity of Phaseolus Caracalla is the produc- 
tion of tertiary bundles of an exclusively phloem-character, while tho 
cambium retains its normal activity. 
Sieve-tubes in the Xylem.J — Prof. E. Chodat discusses the origin 
of the sieve-tubes which occasionally occur in the xylem of woody 
plants, especially in reference to two species of Bicella from Paraguay, 
belonging to the Malpighiacese. He states that the origin of these 
sieve-tubes varies. In Bicella and Atropa they belong to the xylem- 
region, and are formed on the inner face of the cambium-zone. In 
Strychnos , on the other hand, they appear on the outer face of a 
generative arc, the activity of which ceases at the end of a certain time, 
while an adventitious arc is formed at the p*eriphery. In Bicella the 
generative layer often produces at the same time sieve-elements on both the 
inner and outer faces by centripetal and centrifugal septation. The 
* Comptes Rendus, cxiv. (1892) pp. 953-5. 
f Malpighia, v. (1892) pp. 372-85 (2 pis.). 
X Arch. Sci. Phys. et Nat., xxvii. (1892) pp. 229-39 (1 pi.). Cf. this Journal, 
1891, p. 618. 
