ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 405 



whether in vacuoles or dissolved in the sap, the part of the plant ex- 

 amined being in all but one or two cases the root. 



Cystoliths in Exostemma.* — M. E. Heckel describes a new type of 

 calcareous concretion which he has found to exist in the genus Exostemma 

 (Rubiace£e). If a tangential section be made of a young branch of 

 JE. floribundum, two concentric cycles of cystolithic cells will be found 

 in the last layers of the cortical parenchyme. Examined under a 

 sufficiently high power, the cystoliths are seen to be in the form of 

 papillae terminating in a point, and five or six in number ; their apices 

 are all turned towards the interior of the cortex, and their bases 

 towards the exterior. Weak acid causes the dissolution of these 

 calcareous masses, carbonic acid being liberated. It was noticed, how- 

 ever, that after the calcareous mass was gone, a small pedicel composed 

 of cellulose remained on the wall to which it had been affixed ; in this 

 respect, therefore, the cystoliths here described differ from those found 

 in Urticacese. Although the author found numerous cystoliths to exist 

 in Exostemma florihundum, in an allied species E. caribseum they were quite 

 absent. 



Oil of Bay-leaves.f — Sig. G. A. Barbaglia has distilled the essential 

 oil contained in the leaves of the bay-tree, Laurus nobilis, and finds it to 

 have the composition GiJI^iO. This may be a substance belonging to 

 the same series as camphor, CmHieO, or it may be a compound with the 

 formula C14H22 + II2O, a point which must be determined by further 

 investigation of its chemical reactions. 



(3) Structure of Tissues. 



Development of Sieve-plates in the Phloem of Angiosperms.J — 



M. H. Lecomte states that the principal researches on the development 

 of sieve-tubes have been by Wilhelm, Janczewski, and Eussow, and the 

 author criticizes briefly the observations of these three gentlemen. By 

 the help of very sensitive and rapidly acting reagents, he was able to see 

 that the membrane destined to become a sieve is not homogeneous, but 

 is formed of a cellulose network. The substance forming the meshes 

 the author calls callus ; this swells when it is traversed by the contents 

 of the tubes, and forms cushions on each side of the septum. If the 

 contents of the tubes are rich in albuminoids, and if the meshes are 

 large, the osmotic action is very active, and the axis of the meshes can 

 be stained by anilin-blue. From the researches of Baranetzki on 

 the thickening of membranes, it appears that in soft parenchyme tho 

 transverse walls of the cells possess polygonal punctations. The sieve- 

 tube is therefore only an exaggerated parenchymatous cell. 



Development of Cork-wings.§ — Miss E. L. Gregory proceeds to 

 discuss the physiology of the development of cork-wings. The earlier 

 researches made on the subject of cork seem to have fixed its use in the 

 plant economy as that of protection, mainly in the way of a substitute 

 for epidermal tissue ; we now, however, include as part of its function 

 the repairing of tissues torn or broken by external or internal causes, 

 and aiding in the regulation of gases and transpiration. 



* Bull. Soc. Bot. France, xxxv. (1888) pp. 400-3 (3 figs.). 



t Atti Soc. Tosc. Sci. Nat., vi. (1888) pp. 181-4. 



1 Bull. Soc. Bot. France, xxxv. (1888) pp. 405-7. 



§ Bot. Gazette, xiv. (1889) pp. 5-10, 37-44. Cf. ante, p. 242. 



188^. 2 p 



