760 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
receptacles for water. (3) Relations between the Morphology and 
Physiology of the Wood. The xylem is regarded as serving for a 
reservoir and conducting path for water ; the annular and spiral vessels 
contributing chiefly to the former, the pitted vessels to the latter 
purpose. 
Internal Phloem in Dicotyledons* — Dr. D. H. Scott and Mr. G. 
Brebner discuss the origin and function of the layer of phloem which 
occurs in the vascular bundles of the stem and root of many Dicotyledons 
on the medullary as well as the cortical side, characterizing the bundles 
termed “ bicollateral.” They regard the principal, though not the 
exclusive, function of the phloem-systems in the root and stem, to be the 
conduction of food-material, and not, as suggested by Frank and Blass, f 
the storing-up of food-material for the fresh formation of wood. They 
find that (in Acantholimon ) an internal cambium is formed in the stem 
at a late stage, either just inside or just outside the protoxylem ; it pro- 
duces a large amount of medullary wood and phloem, with inverted 
orientation. In the majority of plants examined with bicollateral 
bundles in the stem, a normal structure of the root was found, the 
medullary phloem in the hypocotyl being continuous with the external 
phloem of the root-system. A certain number of roots among the plants 
of this class examined had interxylary strands of phloem, and these may 
be either primary, secondary, or tertiary. Intraxylary (medullary) 
phloem has so far been found only in the roots of Strychnos and 
CJiironia. 
Equivalence of the Vascular Bundles in Vascular Plants.j: — M. 
P. A. Dangeard proposes to establish the equivalence of the vascular 
bundle in all vascular plants. Among Dicotyledons the bundles are 
collateral, and are either closed or open. Among Monocotyledons, 
collateral bundles also occur, as well as concentric, in which the phloem 
is surrounded by the xylem. The difficulty, however, in understanding 
the vascular bundle is in those of Vascular Cryptogams and those of the 
root. The equivalent of the closed bundle of Dicotyledons is to be 
found in the single-veined leaves of Selaginella , Lycopodium , and Tmesi- 
pteris , and in the final ramifications of the veins in the leaves of Salvinia , 
Marsilea, ferns, &c. The bundles are here generally concentric; but, 
contrary to the structure in Monocotyledons, it is the phloem which 
surrounds the xylem. To find the equivalent of the open bundle of 
Dicotyledons and Conifers, we have to look in the stem of certain 
species of Selaginella , such as S. Krausiana, Galeottei, Lyallii , &c. 
Structure and Growth of the Apex in Gymnosperms.§ — Herr L. 
Koch has carefully examined the structure and mode of growth of the 
apex of the branch in a number of Gymnosperms. The method of obser- 
vation employed was the preparation of a large series of excessively thin 
sections by the microtome, after imbedding in paraffin in the mode 
recommended by the author. || The species examined were Tsuga cana- 
densis , Picea excelsa and orientalis , Abies alba , Larix decidua , Cedrus 
* Ann. of Bot., v. (1891) pp. 259-300 (3 pis.). 
f Cf. this Journal, 1890, p. 622. % Comptes Rendus, cxii. (1891) pp. 1228-30. 
§ Jahrb. f. Wiss. Bot. (Pringsheim), xxii. (1891) pp. 491-680 (5 pis.). 
II Cf. this Journal, 1890, p. 674. 
