64 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
of the alburnum in the trunk of trees, but chiefly through the last annual 
ring, which is in direct connection with the appendicular organs of the 
same year. 
Transpiration.^ — Herr 0. Eberdt sums up the results of recent 
researches on this subject, confirming some of the conclusions by 
independent observations. The work is divided into the following 
chapters: — (1) Influence of light on transpiration; (2) Influence of 
the moisture of the air on transpiration; (3) Influence of heat on tran- 
spiration ; (4) Influence of concussion on transpiration ; (5) Influence of 
wind on transpiration ; (6) Periodicity of transpiration. 
V* * * § General. 
Epiphytes.f — Prof. K. Goebel sums up the known facts with regard 
to the life-history of tropical epiphytes. At the end of the root there 
is formed an attachment-disc with root-hairs similar to that of the 
Loranthaceee. In Terniola (Podostemonacese) the attachment to stones 
is effected by a “ thallus ” composed of coalesced dorsiventral branches. 
In Clusia and some species of Ficus, the aerial roots coalesce into a 
cylinder surrounding the stem of the host. The velamen of Aroideae and 
Orchideae is regarded by the author mainly as an grgan of assimilation, 
the absorption of moisture being only a secondary function. In some 
Bromeliaceae, as Tillandsia usneoides, the leaves absorb water directly 
through their surface, and the roots then often completely disappear. 
The absorption of water through the auricles of epiphytic Hepaticie and 
by the leaves and stem of epiphytic ferns and flowering plants, and the 
accumulation of humus by the leaves of ferns specially constructed for 
the purpose, previously described by the author, ^ are now treated of 
more in detail. 
Succulent Plants.§ — In an exhaustive account of the structure and 
biology of succulent plants, Prof. K. Goebel describes the vegetation of 
the “ catingas,” in which the trees are bare of leaves during the dry 
season in the summer. The resistance of succulents to desiccation 
depends not only on their anatomical structure, but also on the mucila- 
ginous character of their sap. Protection against animals is atforded 
either by mechanical means — the thorns of Cactus, or a coating of wax ; 
or by chemical means — alkaloids, tannin, poisonous substances, or latex. 
Extrafloral nectaries occur in some species of Cactus. 
Succulents may be classified into those with succulent leaves, and 
those with succulent stem. Of the former class, when the leaves 
resemble ordinary leaves, as in Oxalis carnosa, it is the upper epiderm 
which assumes the character of hydrenchyme or a reservoir of water ; in 
other cases the hydrenchyme is surrounded by chlorophyllaceous cells. 
In Crassulaceae the hydrenchyme is wanting. 
Stem-succulents occur in the Euphorbiacese, Cactacem, and Ascle- 
* ‘ Die Transpiration rl. Pflanzen u. ilire Abhangigkeit v. ausseren Bedingungen,’ 
Marburg, 1889, 98 pp. (2 pis. and 2 figs.). See Bot. Centralbl., xxxix. (1889) p. 257. 
t ‘ Pflanzenbiologische Schilderungen,’ Pt. i., Marburg, 1889, pp. 147-239 (3 pis. 
and 37 figs.). Cf. this Journal, 1889, p. 414. 
% Cf. this Journal, 1888, pp. 90, 92. 
§ Pflanzen-biol. Schild., Pt. i., Marburg, 1889, pp. 23-110 (4 pis. and 46 figs.). 
