399 
Physiology of Pulpy Fruits. 
ation proceeds, the cells of the pulp become rounded off, and 
only remain in contact at points to which the change has not 
extended. These spots are especially those which appear in 
younger fruits as pits, and the pit membrane resists the 
pressures tending to split it apart, and thus are produced the 
c glove-finger ’-like extensions of the walls of the cells at these 
places when the rest of the middle lamella around them is 
swelling in thickness as degeneration proceeds. The presence 
of these sound parts of the cell-wall is interesting, since, as 
will be seen later, essentially the same thing occurs in Hedera. 
The (now) free surfaces of the cells which bound the inter- 
cellular spaces are seen to be coated with a brown mass, which 
is somewhat rugose on the surface — exactly the appearance 
one would expect to find from the manner in which the cells 
become isolated. 
It will be seen that while the final results, namely cell- 
separation, are the same both in Hedera and Crataegus , the 
latter differs from Hedera in the great completeness with 
which the whole process can be followed out. It is probable 
that the nature of the process is really identical in the 
two cases, only that in the latter plant the thinness of the 
walls makes accurate observation difficult. There is, however, 
in Hedera a true mucilaginous degeneration of the cell- wall, 
which occurs later, and which will be described in its proper 
place, mention being made of it here for the purpose of 
avoiding confusion, as its visible occurrence is subsequent to, 
and could not be traced as a condition of, cell-separation. 
But there is a further cause of irregularity in the cell- 
arrangement of the peripheral layers of the fruit, and this 
cause consists, not in the arrest, but in the increased activity 
of growth in individual filaments. Hence, owing to the strong 
tendency of the other cells to preserve their chain-like arrange- 
ment, the growing cell-row pushes its end in between 1 the 
rows of already formed and still growing rows, and drives 
them apart. The intruding portions may either be the ends 
1 Cf. Krabbe, Das gleitende Wachsthum b. d. Gewebebildung d. Gefasspflanzen. 
188 6. 
