41 8 MILK VESSELS. PART n. 



especially to the layers of the bark, where they take the 

 form of long reticulated perpendicular ducts, through 

 which the proper juices descend towards the roots. 



Each plant has its own system of milk vessels, and 

 M. Lestiboudois has found that the coloured liquids 

 have a rapid motion ; the movements are very compli- 

 cated, not from point to point, but in such a manner 

 that the granules are carried by the liquid into all the 

 ramifications of a complicated network. 



The septa, or divisions between the primordial cells, 

 exert a powerful influence upon the substances con- 

 tained in the sap as it permeates through them, no 

 doubt acting as a dialysing membrane, which separates 

 the gelatinous from the crystalloid matter. The latex 

 is probably separated from the sap by the septa in the 

 cells of the leaves, and sent into the vessels peculiar to 

 it, and then, while the sap is descending and passing 

 through the cambium, it is likely to be dialysed by the 

 septa between the cells of that layer, arresting the pro- 

 tein, and other gelatinous substances, and allowing 

 sugar, starch, and other crystalloid matter to pass 

 freely, and form deposits of organic compounds for the 

 following year. For perennial plants in extra-tropical 

 countries remain in a dormant state during the winter ; 

 their cells are then full of organic compounds under 

 the form of protein, as well as sugar, gum, &c., but 

 especially starch, which is converted into sugar or dex- 

 trine, when spring awakens the plants to renewed life 

 and activity. 



The composition of inorganic matter is very simple ; 

 there are comparatively few radicals, and the substances 

 are compounded of few equivalent atoms, at most eight 

 or ten, sometimes only two or three. Carbonic oxide is 

 formed of one atom of carbon and one of oxygen ; car- 

 bonic acid is formed of one atom of carbon and two of 

 oxygen ; and acetylene, M. Bertholet's base of synthetic 

 compounds, contains two atoms of carbon and two of 



