BOTANY: H. H. M. BOWMAN 
687 
out as long as the source of moisture in the sand is constant and there 
is enough reserve food in the hypocotyl, but the tiny leaves are soon 
burned up by the fierce sunlight and the drying winds. This putting 
out of leaves happens repeatedly until the little seedling is exhausted 
and it succumbs to the hard conditions on the beach. The same thing 
occurred in the full-sun cultures, so that no leaves could be secured on 
which to take transpiration records. 
The method of securing the records was that of Stahl — that is, a 
colorimetric method. A Ganong leaf-clasp was employed and the 
rate of transpiration was measured in minutes and seconds until the 
cobalt chloride paper in the clasp was changed to a uniform pink, due 
to the water given off through the epidermis of the leaf, chiefly that of 
the lower surface, as there are no stomata on the upper surface. Potom- 
eter records were also taken, but on account of the limited amount 
of cultures this method was not feasible. The plants in the soil and 
water concentration cultures could have repeated tests taken on them 
by the Stahl method, whereas for a potometer record a plant would 
have had to be sacrificed for every reading. The readings were taken 
mostly during the middle portion of the day, to secure as uniform con- 
ditions as possible. Some potometer records were made to check up 
results and to get some quantitative idea of the amounts of water really 
transpired. 
In tabulating the results of this work it is found that by plotting these 
transpiration readings (given below in part) with the time intervals as 
ordinates and the concentration percentages as abscissae, a parabolic 
curve is described. The following is a statement of the solution con- 
centrations and transpiration intervals: 
Series A, 100 per cent fresh, 1 . 6 minutes 
Series B, 75 per cent fresh, 1 . 7 minutes 
Series C, 50 per cent fresh, 2 . 4 minutes 
Series D, 20 per cent fresh, 2.8 minutes 
Series E, 10 per cent fresh, 3 . 2 minutes 
Series F, 5 per cent fresh, 3.9 minutes 
Series G, 100 per cent salt, 4 . 1 minutes 
By applying the formula F = CZ«, the constant being the initial 
quantity of water needed to affect the transpirometer, it is also deduced 
that the additional time required for the transpiration of equal quanti- 
ties of water is due to the retarding effect of progressively higher salt 
concentration of the medium — that is, the time factor is a function 
of the square of the concentration divided by a constant. In other 
words, the rate of transpiration varies directly with the concentration 
of the medium in which the Rhizophora plants grow. 
