1910] +REED—TRANSPIRATION AND GROWTH OF WHEAT 85 
times in melted paraffin (0), the pot is filled slightly above the edge of 
the paraffined rim with soil which has received enough water to place it 
in optimum condition (c). ‘The pot is then dipped in melted paraffin 
with intermediate cooling until a firm wall is formed (d). At the first 
_ dipping the paraffin penetrates a short distance into the soil and thus 
cements the outer surface of the mass of soil to the wall of the pot. 
A straight, shallow furrow is then made across the surface of the soil 
and the seeds planted in it. In the present work, where wheat 
Was used, it was previously soaked in tap water until undoubted 
signs of germination were shown and seven seeds were planted in each 
pot. If seven plants appeared’ above the surface of the soil, one 
was subsequently removed, leaving six to grow in each pot. It is 
advisable to cover the surface of the soil in the pot with a layer of 
clean sand to prevent a crust from forming on the soil, as well as to 
aid in uniformly distributing the water which is added. The pots 
are carefully weighed on the day of planting, when the soil is in the 
optimum moisture condition, and their weight recorded. A few 
days after the plants appear above the surface of the soil, the pot is 
Sealed by covering the top with a circular piece of paraffined paper 
provided with a narrow slit in a position which allows the row 
of plants to pass. The paper is sealed to the inner surface of the 
wall of the pot with paraffin. Such a pot is shown at e in jig. 1. 
The pot is weighed immediately before and after sealing, and the 
mctease of weight due to the addition of paper and paraffin is added 
to the initial weight recorded as the “ optimum” for each pot. The 
paraffined paper prevents the loss of all but a very slight amount 
of moisture by evaporation from the soil. Since it is transpiration 
relative to control cultures and not absolute transpiration which was 
determined, the small amount of water lost through the slit may be 
neglected. Thereafter distilled water is added in sufficient quantity 
at intervals of three or four days to keep the weight of the pots 
near that of the original. When water was required by the pots, it 
Was introduced through the slit in the paraffined paper cover by 
Means of a pipette. 
_ One of the conspicuous points of superiority which the paraffined 
Wire pot possesses over the ordinary pot with a non-adhesive wall 
1S shown in fig. 2. In experiments of this character, where the effect 
