THE PHYSIOLOGY OF THE POLLEN OF TRIFOLIUM 
PRATENSE 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 175 
J. N. MARTIN 
(WITH ONE FIGURE) 
The investigation of red clover pollen was begun with the hope 
that a thorough knowledge of its physiology, in conjunction with the 
history of the embryo sac, might help to overcome the uncertainty 
of clover seed production. The investigation was started at the 
University of Chicago during the summer term of 1912 and 
continued at Ames during the autumn of the same year. Many 
points demand further investigation, but the author thought it 
well to publish at this time, since the work cannot be resumed until 
the next growing season. The work has to do with three questions: 
conditions necessary for the germination of pollen; the stigma as a 
stimulative and directive factor in tube development; and relative 
potency of the pollen in self and cross-pollination. - 
Historical 
HAnscirc (8) and Liprorss (9, II) succeeded in germinating 
the pollen of many species in tap water or moist air. The pollen 
of Trifolium hybridum germinated in moist air, but the pollen of 
T. pratense burst. RrrtincHAvs (5) found that the pollen of a 
large number of species would germinate in cane sugar solutions. 
The optimum concentrations for the different species varied from 
20 to 40 per cent. Max Prunprt (14) showed that 20 to 50 per 
cent concentrations were required for the pollen of some grasses. 
Kny (3) found that the pollen of Aesculus Hippocastanum, 
Lilium bulbiferum, Robinia Pseudo-Acacia, Lathyrus tuberosus, 
and Pisum sativum germinated better when gelatin was added to 
the cane Sugar solution. MAncrn (4) increased the germination in 
some species by adding either agar or gelatin to the sugar medium. 
Jost (12) found the germination of the pollen of some species 
of grasses to depend entirely upon the water supply. This he 
Botanical Gazette, vol. 56] [112 


