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difference as to the period when they fall, or as to the weight 
requisite to detach them. The influence, then, of the axillary 
buds in detaching leaves in autumn (a very different matter 
from the separation of the persistent leaves in spring by the 
same organs), would seem to be nil, and we may turn to other 
assigned causes. Among these are the formation of earthy or 
mineral materials in the tissues of the leaf, to such an extent as 
to block up the cells and impede their action. That such an 
accumulation does take place, is easily proved by chemical 
analysis and microscopical observation. The latter shows a 
much larger proportion of raphides or crystalline deposit in the 
cells in the leaves about to fall than at other times. The 
falling leaves of the common cherry laurel, Prunus lauro- 
cerasus , may be cited as affording a good illustration of this 
accumulation of raphides, the more so as the leaves of this 
plant, as of most of the so-called evergreens, are not shed in 
greater numbers at the approach of winter than at any other 
time, but are irregular in this respect. The accumulation of 
earthy matters in the leaves serves to restore to the ground in 
some measure the mineral ingredients taken from it by the 
growing plant ; hence the impolicy of the practice, so often 
followed in gardens to the detriment of the shrubs, &c., of re- 
moving the fallen foliage from the soil ; if such be necessary for 
purposes of neatness, some other provision should be made to 
supply the soil with what is requisite for the growth of plants. 
The storage in largely increased quantities of starch granules in 
the cells, has also been noted by Dr. Inman and others, as 
taking place in leaves just previous to their fall; and it is easy 
to conceive that the distension of the tissues, and the impedi- 
ment offered to the due discharge of their functions, might 
facilitate the separation of leaf and stem. 
But in the face of the facts already mentioned, and especially 
when it is recollected how very “ clean ” is the fracture between 
the leaf-stalk and its attachment, how it is nearly as even and 
smooth as if the severance had been made with a knife, it be- 
comes evident that whatever influence the circumstances before 
mentioned on the phenomena in question may have, they can 
but be secondary and indirect, and we are driven to seek some 
cause in the organisation of the leaf itself. At one time it was 
considered that the varying direction of the several layers of 
tissue in the leaf-stalk would account for their separation, and 
this would seem borne out by the very common arrangement of 
the w r ood cells of the leaf-stalk, nearly at a right angle to the 
cellular tissue. This arrangement may be seen in many leaves, as 
in Rhus typhinum, Gleditschia , &c., but according to Von Mohl, 
it is far from being general. Schacht’s notion was, that the fall 
of the leaf was due to the gradual intrusion of a layer of cork 
