108 DR. K. LEDEGANCK ON THE FALL OF LEAVES IN AUTUMN. 



layers, which cause the peeling off of the epidermis of the 

 stem. 



The detailed examination from direct observation, the micro- 

 chemical studies which we have been enabled to make, and the 

 consequent deeper insight into the nature of these different tissues, 

 their changes in autumn, are what we have to offer for your 

 consideration. 



IV. — Histo-Chemical Researches* 



Dr. Ledeganck then gives, at considerable length, his researches 

 on the following subjects, which, although of great interest, are too 

 long for insertion here : — 



Obs, 1. Betula.alba, and Fagus sylvatica. 

 Ulmus campestris. 

 do. 



2. 

 3. 

 4. 



5. 



6. 



7. 



8. 



9. 

 10. 

 11. 

 12. 

 13. 

 14. 



do. 

 Eibes grossularia 

 Syringa vulgaris 



do. 

 Tilia europ^ea 

 Populus alba. 

 Betula alba 

 Fraxinus Ornus 

 Juglans regia 

 Quercus Eobur 

 Carpinus Betulus 



V. — Special Observations. 



There is one thing which above all needs explanation, that is 

 the mode by which the rupture of the central vascular bundle is 

 produced ; whether the periderm is in form of layers or scattered 

 cells, we have never seen the process of suberification break through 

 the tissues constituting the vascular bundle of the axis. Some- 

 times it may be seen above the level of the scar, at other times 

 below, but in most cases it will be found broken at the surface. 

 Besides, in most cases, where the leaf separates spontaneously, 

 we see the periderm form an uninterrupted layer upon the cicatrix, 



*Autlior's Note. — Not being able to relate in extenso the whole of our observa- 

 tions which bear upon a great number of species, we limit ourselves to extracts 

 of which the results appear to us the clearest and most conclusive. 



