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B. F. LUTMAN 
of turgor in these peripheral leaf cells. The bean and the corn plants were 
found to have a higher osmotic pressure in the stalks, and these plants do 
not often suffer from wilting of the tips and margins of the leaflets (with 
the resultant tip-burn) as do those of the potato plant. Several reasons 
may be given for this difference. The bean leaves in intense sunlight assume 
such a position that their laminae are parallel to the eight rays while the 
corn leaves roll up in intense heat. Neither of these plants is as succulent 
as the potato; the loss of water between adjacent cells ought to be very 
small as compared with that between the potato cells. The real cause for 
tip-burn in the potato may lie, too, in the movement of the elaborated food 
materials. 
3. A high osmotic pressure does not seem to be necessary for the growth 
of reproductive organs nor for the continued deposition in them of reserve 
carbohydrates, such as starch or sugar. The sugar beet or the garden 
beet ought to be able to withdraw elaborated food materials from the leaves 
by osmotic pressure since their pressure is greater than that of the leaves. 
If these materials were put into the proper channels, they ought to find 
their way by osmosis to the storage organ. The continued growth of the 
potato tuber continues, however, when its osmotic pressure is only between 
6 and 9 atmospheres, and at no time is the pressure greater in the tuber 
than it is in the leaves. The stalks record even a greater pressure than do 
the leaves. The movement of food materials is undoubtedly due to dif- 
ferences in osmotic pressures, but the manner in which they work to induce 
the flow of carbohydrates to the tubers is, as yet, unexplained. 
The stalk of the plant seems to serve as an organ for temporary storage 
if the amount of sugar in it during periods of active carbon assimilation is an 
indication. Elaboration processes probably occur here but their nature is 
almost entirely speculation. The further translocation in the potato plant 
is dependent on the age of the plant; early in its growth, the material is 
used for the production of new leaves, but after the formation of the young* 
tubers, the current changes its direction and the materials flow into them. 
The translocation of these carbohydrates probably occurs largely through 
the sieve-tubes according to the plant physiologists who have studied this 
phase of the subject; see Pfeffer (13, pp. 575-583) and Haberlandt (8, 
pp. 328-336). Neither of these authors, however, explains on the basis of 
experimental evidence the means by which the carbohydrate compounds 
are moved. Haberlandt (p. 334) makes the following statement concerning 
protein compounds: "When a petiole or stem of Cucurbita is cut across, 
large quantities of slimy protein-material exude from the several sieve- 
tubes. With reference to this point, A. Fischer has proved that the effects 
of a cut petiole extend through one or two internodes at the very least. 
This observation indicates that the pressure in the sieve-tubes is sufficient 
to overcome the resistance opposed by a very considerable number of sieve- 
plates. Thence we may infer that any differences which arise within the 
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