820 SUMMARY OF CURRENT RESEARCHES RELATING TO 



is insoluble in the cell-sap does not rest on a satisfactory basis ; in 

 some cases, on the contrary, it would certainly appear to be dissolved, 

 and in this state to pass through the cell-wall. It is, however, 

 soluble with difficulty ; and the function of oxalic acid seems to be 

 to get rid, in this form, of what would otherwise be an injurious 

 excess of lime. Lime and oxalic acid are both present in soils in 

 greater quantity than is needed by the plant ; and their excess is 

 consequently excreted by the plant in an insoluble form, or at least 

 one that is soluble only with difficulty. 



Function of Resinous Substances.* — H. de Vries has investi- 

 gated this subject in detail, especially in reference to the terebenthin 

 and resin produced by conifers ; and urges arguments in opposition 

 to the generally accepted view that these substances are simply waste 

 products of an excretory nature. Terebenthin is the substance most 

 rich in carbon which occurs in conifers, and its production requires, 

 in consequence, the consumption of a relatively large quantity of 

 assimilated substances, especially of glucose, from which it is probably 

 formed only by a long series of chemical transformations ; and its 

 production can in no sense be regarded as analogous to that of gum 

 in wounded cherry or plum trees. It must, on the contrary, be looked 

 on as a normal and important function in the life of conifers. As 

 long as the reservoirs in which it is formed remain closed, this resin 

 undergoes no change ; but whenever the organ is wounded, it flows 

 out in the form of a thick viscid mass, which gradually hardens on 

 exposure to the air. But it not only spreads over the surface of the 

 wound, it penetrates also to the interior of the wood, fills the cell- 

 cavities, and saturates the cell-walls. 



According to their direction, the resin-canals of the wood and 

 bark of conifers may be classified into horizontal and vertical ; the 

 former are found especially in the medullary rays. 



Briefly, the object attained by conifers in sacrificing so large a 

 quantity of food-material in the production of resinous secretions, is 

 the acquisition of a substance which furnishes a complete remedy 

 against a great variety of injuries to which the woody tissues are 

 subject. 



The author then investigates the functions of similar secretions 

 formed by other orders of plants, especially that of resinous sub- 

 stances, gums, and latex. The entire absence of substances of this 

 nature in large groups of plants, as the Palmse, Cyperacese, Gramineae, 

 and the greater number of Cruciferaj and Ranunculacese, indicates 

 that their function must have relation to special circumstances. That 

 the function of all these substances is similar is further indicated by 

 the fact that they replace one another in different plants or groups of 

 plants, it being very unusual to find more than one kind in the same 

 species. Again, under normal conditions, they are never resorbed 

 out of their reservoirs to take part in other nutritive processes ; as 

 long as they remain in their reservoir they are completely inactive. 

 In this situation they are always subject to a certain pressure which 



* Arch. Neerland. Sci., xvii. (1882) pp. 59-82. 



