1913] MARTIN—POLLEN OF TRIFOLIUM PRATENSE 115 
dissolved in a liter of water) and calculated for 25° C. according to 
data and formulae given by RENNER (18), it gives an osmotic 
pressure of 163.5 atmospheres. This takes no account of the 
excessive increase of pressure over concentration between 4.13 and 
4.65 weight-normal (2.33 volume-normal). The pollen was per- 
meable to saturated solutions of KNO, and NaCl, and these salts 
could not be used for determining osmotic pressure. 
Germination of pollen 
The pollen of Trifolium pratense bursts almost instantly when 
dropped into water, so any suitable medium must control water 
absorption. Small amounts of sugar solutions made up in double 
distilled water by the volume-normal method were used in the 
ordinary watch glasses, carefully cleansed. The flowers were 
collected between 9 A.M. and 3 P.M. and the pollen from those well 
open, but still fresh, was used. The dishes, sealed with glass plates 
and vaseline, were left on the laboratory table and observations 
were made about every 30 minutes during the three or four-hour 
test period. Table IL shows the effects of different sugar solutions 
on the pollen of Trifolium pratense, T. hybridum, and T. repens. 
Decoctions of the stigmas alone or in distilled water, as well as 
those made by grinding the stigmas in the sucrose and levulose 
solutions given in table II, gave no germination in Trifolium 
pratense; 0.000075, 0.000375, and 0.075 volume-normal solutions 
of malic acid, as well as equal concentrations of calcium malate, 
added to the sugar solutions gave increased bursting in T. pratense 
and reduced the percentage of germination in T. hybridum and 
T. repens. A 0.000277 volume-normal of HCl or a 0.00056 
volume-normal of butyric acid used with the sugar solutions had 
little effect. The butyric acid gave a little better germination in 
T. hybridum and T. repens in sucrose solutions above 0.731 volume- 
normal. Stronger solutions of either acid increased bursting and 
cut down germination. Sugar solutions containing agar or gelatin 
allowed less bursting, and 2 grams to 5 grams of gelatin added to a 
©. 731 volume-normal solution of sucrose gave the best medium for 
the pollen of T. hybridum and T. repens. Pollen of T. pratense 
run in sugar solutions under increased pressure of oxygen and 
