984 SUMMARY OF CURRENT RESEARCHES RELATING TO 



C3] Secretions. 



Secretion of Araucaria.*— MM. E. Heckel and P. Schlagdenhauflfen 

 have demonstrated an interesting fact in regard to the secretion of Araucaria. 

 The secretions of Conifers are known to be oleoresins, consisting of an 

 essential oil and of a resin. But in the section Araucariese, it would 

 appear that the secretion is not a resin nor an oleoresin, but a resinous 

 gum. The observations proving this interesting exception vrere made on a 

 large number of Araucarias, so that the fact may be safely affirmed as true 

 of the genus. The chemical investigations, the details of which need not be 

 repeated, were based especially on the exudations of Araucaria Coohi R. Br. 

 It is interesting to find a distinct genus thus marked off by chemical as 

 well as morphological peculiarities. 



C4) Stractiire of Tissues. 



Aquiferous Tissue in the Leaves of Sansevieria.f — A similar function 

 to that of the peculiar structures in the roots of austral ConifersB is, 

 according to Prof. F. W. 0. Areschoug, exercised by certain cells with 

 fibrous thickenings in several species of Sansevisria. Almost the whole of 

 the internal fundamental tissue of the very thick leaves is transformed into 

 aquiferous tissue, except a portion immediately surrounding the vascular 

 bundles. The cell-wells of this tissue are very thin and porous, the pores 

 having the form of a flat ring. The whole of the inner surface, even of the 

 horizontal walls, is covered by slender branching fibre-like thickenings 

 arranged spirally, which prevent them from contracting, so that they may 

 serve as a perpetual reservoir of water. 



Laticiferous Vessels and Assimilating System. | — From an examina- 

 tion of the orders Apocynaceaa, AsclepiadesB, EuphorlDiaceae, Campanulacesa, 

 and Lobeliacese, Sigg. J. E. Pirotta and L. Marcatilli endeavour to trace 

 the relationship between the laticiferous vessels and the assimilating 

 tissue in the leaves. They find that, in the greater number of cases, the 

 laticiferous vessels follow the course of the veins, and form in the leaves a 

 more or less close network. In other cases they leave the veins and spread 

 through the mesophyll. In all cases the authors believe that the latici- 

 ferous vessels are so arranged as to receive the products of assimilation 

 from the parts where they are elaborated and transport them to the different 

 parts of the plant. 



Sieve-tubes.§ — Dr. A. Fischer defines a sieve-tube as active so long as, 

 on making a section of the living plant, it forms " Schlauchkopfe," i. e. so 

 long as the sieve-pores are open and the contents fluid. Of active sieve- 

 tubes he distinguishes three kinds, viz. (1) With coagulable sap ; the 

 contents consist of a slight parietal layer of protoplasm, and a clear sap 

 which coagulates on heating (CucurbitaceaB). (2) With mucilage ; the 

 contents consist of a delicate parietal layer of protoplasm with a larger or 

 smaller admixture of mucilage, and a clear watery not coagulable sap 

 (Humulus). (3) With starch-grains; the contents consist of a delicate 

 parietal layer of protoplasm containing a small quantity of mucilage, and a 

 clear not coagulable sap with starch-grains (Coleus). Most Dicotyledons 

 belong to the third type ; the rest, with the exception of Cucurbitaceaa, to 



• Comptes Kendus, cv. (1887) pp. 359-60. 



t SB. Bot. Verein Lund, March 17, 1887. See Bot. Gentralbl., xxxi. (1887) p. 258. 



i Annal. 1st. Bot. Roma, 4 pp. See Bull. Soc, Bot. France, xxxiv. (1887), Kev. 

 Bibl., p. 51. 



§ Ber. K. Sachs. Gesell. Wiss., 1886, 48 pp. and 2 pis. See Bot. Gentralbl., xxxi. 

 (1887) p. 8, (Jf. this Journal, 1886, p. 268. 



