604 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Occurrence of the Elements of Sugar of Milk in Plants.* — 



Acconliiig to M. A. Miiiitz, tlic mucous siibstanccs of plants^gums, 

 mucilages, poetic substances, &c. — contain, in the products of their 

 doubling, galactose identical with that of sugar of milk ; and these 

 mucous substances exist in vegetable food-materials in such quantities 

 that they are able to supply the galactose which enters into the com- 

 position of the sugar of milk secreted by the mammary glands of herbi- 

 vorous animals. 



Development of some Secretions and their Receptacles.! — Herr 

 A. Tschirch calls attention to the diiferent origin, in the general way, 

 of gum, which is a pathological product and the result of the disor- 

 ganization of the cell-wall, and resin, which is formed in the cell-cavity 

 in the bark and wood, diffuses through the cell-walls, and is secreted 

 into the intercellular passages by a thin- walled tissue, the "secreting 

 epithelium," which clothes the schizogenous canals. There are, how- 

 ever, instances in which gum or mucilage occurs as a cell-content, as in 

 Orchis, or is excreted into schizogenous receptacles, as in the Cycadeae ; 

 and, on the other hand, instances in which the cell-wall takes part in 

 the formation of ethereal oils and resins, as in the lysigenous oil-passages 

 of the Aurantiacepe. 



The author then describes the method of formation of copaiva-balsam, 

 which takes place, not in schizogenous, as sometimes described, but in 

 lysigenous canals. The absorption of the cell-walls, and the formation 

 of the resin, commence in the parenchyma of the wood, advancing from 

 there to the medullary rays, the libriform, and the vessels. In Styrax 

 Benzoin also, the source of the benzoin of commerce, the resin is not 

 formed in schizogenous canals, but originates in the medullary rays, 

 advancing from them to the surrounding phloem-parenchyma, and finally 

 to the bast-cells and sclereides. The same is, in general terms, the 

 history of the formation of the resin in Ahies, Thuja, and Dipterocarjms. 



In the so-called myrrhs, on the other hand, species of Bahamea and 

 Boswellia, the gum-resin is always formed in schizogenous receptacles or 

 in true cells. 



(3) Structure of Tissues. 



Secretory Canals and Secretory Reservoirs.^ — M. A. Leblois gives 

 a detailed account of the origin and development of secretory canals and 

 secretory reservoirs. 



The paper is divided into four portions :— (1) Those families which 

 possess only secretory reservoirs : — e. g. Myoporese, Myrtaceae, Rutaceas, 

 and Myrsinese. (2) Those which possess both secretory canals and 

 secretory reservoirs : — e. g. Compositae, Hypcricacere, Clusiaceae, and 

 Aroidea). (3) Those which possess only secretory canals : — e.g. Canneae, 

 AnacardiacePB, Simarubeae, Pittosporeao, and Butomeae ; and (4) Study of 

 laticiferous vessels. 



In conclusion, the author states that the tissue which has been 

 studied in this paper is a living tissue. It arises always in the same 

 manner, by division and dissociation, and not by the destruction and 

 resorption of cells. It is a secretory tissue, and it presents itself in two 



• Ann. Chim. et Phys., x. (1887). See Bull. Soc. Bot. France, xxxv. (1888) 

 Bev. Bibl., p. 11. 



t Bcr. Deutsch. Bot. Gesell., vi. (1888) pp. 2-13 (1 pi. and 1 fig.), 

 i Ann. Sci. Nat. (Bot.), vi. (1S87) pp. 245-330 (5 pis.). 



