40 8 Farmer . — On the Morphology and 
already described for Sambucus nigra \ only that here the 
‘ slipping ’ takes place to a far greater extent, and the later 
addition, so remarkable in Sambucus , is entirely wanting in 
Rubus. Lignification sets in very early in the cells of the 
endocarp, and results in the conversion of the entire tissue into 
the well-known hard shell which encloses the seed of so many 
drupes. Markings of a pitted character may be detected in 
these fibres, whose walls thicken to such a degree as to almost 
obliterate the cell-lumen ; but as we shall see later, many 
other fruits exhibit these markings in a state of much greater 
perfection. 
At a stage subsequent to that at which the endocarp has 
become clearly recognisable, the character of the cells at the 
periphery of the fruit begins to change and the limits of the 
epicarp are defined. I have already mentioned the fact that 
exclusive of the endocarp, the cells are roughly arranged in 
radial rows, each containing about eight to ten cells. The 
outer four or five of these become gradually flattened radially, 
and consequently extended tangentially, whilst their walls 
also are thickened as the process of distortion takes place. 
The cells which are thus displaced from their originally 
regular position, form an interlocking mass of a very tough 
texture, and this mass represents the removeable skin which 
encloses the softer portions of the fruit. Internally the cells 
pass by a somewhat sudden transition into the pulp, which 
must now be considered. At the inner boundary of the epi- 
carp, which consists, as I have said, of flattened elements, there 
is a layer of cells which are of an approximately isodiametric 
shape, and whose walls, unlike those of the cells of the epicarp, 
are exceedingly thin. This layer forms the outer boundary 
of the mesocarp or pulp proper. 
As would be expected from the conditions under which the 
separate drupelets are placed, the mesocarp does not surround 
the endocarp as a layer of equal thickness throughout, but is 
developed to the greatest extent on the free portions where 
1 Ann. Bot. vol. ii. p. 389. 
