CHANGES IN THE CHLOROPHYLL OF LEAVES IN AUTUMN. 319 



at the end of a period of vegetation ; hut that it is conveyed into the persistent 

 reservoirs of reserve-materials, which put forth shoots again at a later period of 

 vegetation. ' The process does not always run the same course in trees of different 

 species. In the Horse-chestnut, for example, as well as in Dioscorea batatas, the 

 form of the chlorophyll-corpuscles is destroyed at the same time as their green 

 colour, and the chlorophyll disappears simultaneously with the starch contained in it. 

 In the Vine, I found that the form of the chlorophyll-corpuscles is first destroyed, 

 while the starch disappears, the green colour of the amorphous chlorophyll being 

 maintained however for some time.' In Sambucus Populus, and Robinia, on the 

 other hand, the starch first disappears from the chlorophyll-corpuscles, while the 

 form and green colour persist for some time longer. In the Mulberry (RIorus 

 alba), the form of the chlorophyll-corpuscles is first destroyed, then the green 

 colour disappears, and finally the matrix together with the starch contained 

 iti it. These observations do not preclude that in the same species of plant the 

 processes in the cells containing chlorophyll may take their course sometimes in 

 the one, sometimes in the other way. It is not always possible to see from the 

 outside whether the autumnal emptying of the leaves has already commenced. 

 When the leaves become pale, however, the destruction of the chlorophyll has 

 already begun ; and when they have turned yellow it is completed. On the other 

 hand, in leaves which are still green in September and October the form of the 

 chlorophyll-corpuscles may be already destroyed, as in the Vine, Poplar, Robinia, and 

 Sambucus. With the general disappearance of the cell-contents, the dissolution 

 of the cell-nucleus and protoplasm, the peripheral chlorophyll-corpuslces lose their 

 normal outlines, assume irregular forms, the contained starch disappears, and their 

 colouring matter undergoea changes : they become pale green. Oil-drops often 

 appear in the cells, the quantity of chlorophyll perceptibly diminishes, the de- 

 formed corpuscles become smaller, and, when they have finally disappeared entirely, 

 a large number of very small granules remain behind in the cell-sap : these refract 

 light strongly and are coloured bright yellow, but they are to be in no way com- 

 pared with the immature yellow chlorophyll-corpuscles of leaves grown in the dark. 

 They often flow together into large oily drops, and evidently form a residuum of 

 no further use in the economy of the plant. It is these yellow granules which 

 cause the autumnal yellow colouring of so many leaves, and which also remain 

 behind in the emptied cells of leaves which turn red in the Autumn ; in this case, 

 however, they lie in a homogeneous red cell-sap. 



The cell-contents of the leaves of plants placed subsequently in the dark 

 undergo very similar changes, which are particularly rapid at high temperatures. 

 And various other circumstances which disturb nutrition, such as persistent drought, 

 or lack of nutritive matters generally, bring about the same processes even in 

 bright light. In all these cases the process described commences in the oldest 

 leaves, and advances to the younger ones ; the leaf-cells remain distended with 

 sap but their volume appears notably to diminish. The emptied cell-skeletons 

 are finally cast off for the most part, since, as Mohl showed in detail, a new 

 layer of cells is formed cutting across the base of the petiole, and preparing 

 the petiole for the fall. Then, with the advent of the first frosty nights at the 

 end of October or the beginning of November, a plate of ice is formed in this 



