Physiology of Pulpy Fruits. 4 1 1 
Solanum Dulcamara . — In the fruit of this plant we meet 
with a case in which the pulp owes its origin to two sources, 
being derived partly from the wall of the superior ovary, and 
partly from the tissue of the placenta. The carpels at the 
time of flowering are somewhat thin structures, containing a 
number of vascular bundles which run at a distance of about 
eight cells from the epidermis, and even at this period there is 
a difference perceptible between the cells which lie outside, 
and those which lie inside, the zone of vascular bundles. The 
former already show a flattening of their cavities like those 
which correspond to them in Rubus , and this appearance is 
accompanied by a slight thickening of their walls. The cells 
of the interior, on the other hand, are fairly isodiametric and 
thin-walled ; they are much distended with cell-sap, and their 
protoplasmic contents become reduced to a thin primordial 
utricle, as may be easily shown by plasmolysing. Those cells 
which immediately bound the cavities of the ovaries are some- 
what smaller than the rest, but they show no marked irregu- 
larity of size. 
At the flowering time, the ovules stand out from the pla- 
centa into the cavities of the bilocular ovary and do not touch 
the carpel-walls, but if fertilization is effected this state of 
things is soon altered. Radial and tangential divisions arise 
in the layers of cells lying beneath the inner limiting layer 
(epidermis) of the carpels, and this process causes an ingrowth 
of the tissue of these bodies into the space left between the 
ovules. At the same time the cells of the placenta also 
multiply and grow larger, though the limit of possible ex- 
pansion of this structure is of course determined by the size 
of the fruit-cavities. The placenta, however, takes advantage 
of all the spare room left between the ovules, and by growing 
out between them, causes them to appear as if they were sunk 
in its substance (PI. XXVI, Fig. 30). Those processes grow 
outwards, enclosing the ovules, until they finally meet with 
the similar ingrowths of the carpels, which likewise penetrate 
between the separate ovules. The two surfaces then become 
pressed together, and the line of demarcation between them is 
