246
GEORGE G. LATIES
vacuum and the vacuum released, the respiration on a unit weight basis
remained independent of thickness, and there was no visible sign of
water injection. Furthermore, when a sheet of potato tissue approximately 5 mm. in thickness was placed in a Seitz filter in place of the
filter pad, it proved impossible to force water through the tissue under
5 atmospheres of pressure. It was considered, therefore, that the air
space in the potato tuber is discontinuous, comprising Jamins chains
wherein minute liquid droplets alternate with air pockets in capillaries
of very small cross-section.
When the diameter of such capillaries is small enough, the capillary
attraction of liquid to the capillary wall is so great that the liquid
cannot be dislodged by one atmosphere of pressure. Air may nevertheless be removed from such tissues by evacuation without disturbing the
liquid barriers. Furthermore, the air pockets expedite diffusion of gases
in such tissue and can be responsible for the over-all diffusion coefficient estimated by Burton. There is thus a further basis for believing
that it is not water injection of potato disks which, by affecting the
oxygen supply, diminishes the specific respiration rate with increasingly
thick disks, when such a relationship is found.
Laties has observed that when potato slices are incubated for 24
hours the relation between thickness and respiration rate described by
Steward becomes evident. It can be readily calculated that in air it is
not simply the higher respiratory rate of incubated tissue which brings
about the dependence of respiration rate on thickness. Furthermore,
pure oxygen does nothing to alleviate the diminution in respiration in
air which occurs as slices are made thicker. Finally, it has been demonstrated that it is the development of the respiratory system which arises
on aging which is sensitive to disk thickness, and not the manifestation
of this system once it has been developed. Thus if cores of potato tuber
are incubated overnight it is the respiration of only the outermost millimeter mantle of tissue which increases in magnitude several fold. The
remainder of the core resembles fresh tissue, albeit there is no evidence
of oxygen limitation upon the respiration of the core. Alternatively,
when a disk 2 mm. in thickness is aged, and the respiratory increment
allowed to develop, there is no effect upon the respiration when the disk
is subsequently sliced into three, and the respiration of the three thin
disks compared to that of the unsliced disk. Since, in the past, experiments designed to test the effect of thickness on respiration rate were
carried out with disks which were aged at various thicknesses, the observed effects of thickness on respiration rate actually reflected the effect
of thickness on the development of one or more new respiration systems.
Experiments by Laties have tentatively ruled out carbon dioxide as the
GEORGE G. LATIES
vacuum and the vacuum released, the respiration on a unit weight basis
remained independent of thickness, and there was no visible sign of
water injection. Furthermore, when a sheet of potato tissue approximately 5 mm. in thickness was placed in a Seitz filter in place of the
filter pad, it proved impossible to force water through the tissue under
5 atmospheres of pressure. It was considered, therefore, that the air
space in the potato tuber is discontinuous, comprising Jamins chains
wherein minute liquid droplets alternate with air pockets in capillaries
of very small cross-section.
When the diameter of such capillaries is small enough, the capillary
attraction of liquid to the capillary wall is so great that the liquid
cannot be dislodged by one atmosphere of pressure. Air may nevertheless be removed from such tissues by evacuation without disturbing the
liquid barriers. Furthermore, the air pockets expedite diffusion of gases
in such tissue and can be responsible for the over-all diffusion coefficient estimated by Burton. There is thus a further basis for believing
that it is not water injection of potato disks which, by affecting the
oxygen supply, diminishes the specific respiration rate with increasingly
thick disks, when such a relationship is found.
Laties has observed that when potato slices are incubated for 24
hours the relation between thickness and respiration rate described by
Steward becomes evident. It can be readily calculated that in air it is
not simply the higher respiratory rate of incubated tissue which brings
about the dependence of respiration rate on thickness. Furthermore,
pure oxygen does nothing to alleviate the diminution in respiration in
air which occurs as slices are made thicker. Finally, it has been demonstrated that it is the development of the respiratory system which arises
on aging which is sensitive to disk thickness, and not the manifestation
of this system once it has been developed. Thus if cores of potato tuber
are incubated overnight it is the respiration of only the outermost millimeter mantle of tissue which increases in magnitude several fold. The
remainder of the core resembles fresh tissue, albeit there is no evidence
of oxygen limitation upon the respiration of the core. Alternatively,
when a disk 2 mm. in thickness is aged, and the respiratory increment
allowed to develop, there is no effect upon the respiration when the disk
is subsequently sliced into three, and the respiration of the three thin
disks compared to that of the unsliced disk. Since, in the past, experiments designed to test the effect of thickness on respiration rate were
carried out with disks which were aged at various thicknesses, the observed effects of thickness on respiration rate actually reflected the effect
of thickness on the development of one or more new respiration systems.
Experiments by Laties have tentatively ruled out carbon dioxide as the