52 THE INNER ORGANIZATION OF TREES. 



in regular order and change their form and color as the 

 metamorphosis of the sap progresses. In herbaceous an- 

 nuals and perennials, a few weeks or months is all that is 

 required to transmute the sap into its final products ; but 

 in perennial ligneous plants, such as shrubs and forest trees, 

 the period of metamorphosis is greatly protracted, and it is 

 sometimes years before the whole thing culminates, and 

 the luscious fruit hangs at last from the branches. 



The recent advances which have been made in Vegetable 

 Anatomy and Physiology, result from the right application 

 of chemical reagents to sections of vegetable tissue, when 

 placed beneath the microscope. The principal reagents 

 employed in these researches are Sulphuric Acid, Iodine, 

 Caustic Potash, Sulphuric Ether, Alcohol, and Ammonia. 

 Through the use of these reagents, a few facts have been 

 brought to light. Starch, for example, is detected by Iodine, 

 if present in the cells, by the blue color which the granules 

 assume. In this manner starch may be readily ascertained 

 to exist in the tubers of the potato and in the milky juice of 

 Euphorbia splendens. It is only necessary to place a thin 

 transparent slice of the tuber of the potato or a single drop 

 of the milk of the Euphorbia, under the microscope and 

 apply Tincture of Iodine, when the granules will imme- 

 diately become visible by the deep blue color which they 

 will take. 



a. Club-shaped granules in milky juice of Euphorbia splendens. b. Three 

 of the lactiferous vessels, with starch granules in situ. QUEKETT. 



In a similar manner, the chemical nature of chlorophyl, 

 the substance which gives to the leaves of plants their green 



