Physiology of Pulpy Frtiits. 405 
starch is also in some cases distinguishable, though only in 
very small quantities. Crystals of oxalate of lime are not 
uncommon, especially near the vascular bundles ; but the most 
interesting of the cell-contents is the oil which is present in 
minute quantities in the protoplasm of all the cells. This 
substance is often only detected with difficulty until the fruit 
is ripe, but careful staining, especially with osmic acid, gener- 
ally succeeds in making it apparent. As the fruits ripen, on 
the other hand, the volume of oil in the cells increases very 
largely ; it forms aggregates of spherical drops of a considerable 
size, which are surrounded by a delicate pellicle of protoplasm, 
which serves to keep the several drops asunder. When it is 
being secreted at this late stage of the development of the 
fruit, it is seen to appear in the first instance as a number of 
excessively small brightly refracting globules, which are em- 
bedded in the substance 1 of the comparatively thin primordial 
utricle. The globules increase rapidly in size and run together 
so as to form larger and larger drops, though each drop is, at 
least temporarily, provided with a membrane which serves to 
separate it from the rest in its immediate vicinity. This limiting 
membrane must disappear between the points of contact of 
drops about to fuse, in much the same way as two soap 
bubbles behave when placed in such a position that their 
cavities are about to unite, for, although I have not actually 
seen the process in operation, it must occur, since the number 
of drops grow less as the actual size gets larger. But besides 
the increase in size caused by running together of the drops, 
there is the active process of secretion going on in the proto- 
plasm, and by virtue of which its own substance is gradually 
used up. The larger drops now project into the cell vacuole 
and soon fill it, while the protoplasm only remains as a thin 
layer lining the cell-wall, and the now large oil drops. Addition 
of potash, especially on warming, causes the oil to run into 
1 Cf. Wakker. Studien ii. d. Inhaltskorper d. Pflanzenzelle ; Prings. Jabhrb. 
XIX. Bd. 1888. I have not been able to trace any structures resembling elaioplasts 
in Hedera , but it is perhaps a significant fact that the chlorophyll-granules are still 
intact during the oil-secretion. 
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