534 Journal of Agricultural Research vo1.xviii.no.io 



What part is played by the Hpoid content of the protoplasm and its 

 spatial relation to the disperse medium in those different colloidal proc- 

 esses we can only surmise, since the chemistry or even the quantita- 

 tive analysis of pollen is not well known. Lloyd (4, 5) infers that there 

 may be such a relation. 



The extreme sensitiveness of the pollen grain of barley to external 

 conditions might be expected to lead to considerable sterility in the 

 field. In most varieties, however, there is very little sterility. This, 

 doubtless, is due to an equally delicate adjustment of the dehiscence of 

 the anther. Development of the anthers seems to be entirely checked 

 on cold, wet days. There may be very little fertilization for two or 

 three days in succession during a period of adverse weather conditions. 

 The development or at least the dehiscence of the anthers is retarded at 

 night as well. In the morning, especially if the morning be clear, there 

 is a very rapid evaporation of the dew and other condensed moisture 

 from the surface of the plant. A little later the anthers begin to dehisce. 

 This rupturing of the anther apparently occurs when its temperature 

 rises and its surface begins to dry. This seems to be the time most 

 favorable for the growth of the pollen as well. Conditions unfavorable 

 for the growth of pollen are unfavorable for dehiscence. 



The large number of anthers breaking in the early part of the fore- 

 noon indicates that those ripening since the preceding day had delayed 

 dehiscence until favorable conditions obtained. After the very active 

 period of the forenoon little fertilization occurs until midaftemoon. 

 It would seem that most of the anthers near ripeness had burst during 

 the favorable period of the morning; and, except in scattering florets, 

 renewed activity had to await the maturation of the next group of 

 anthers. It is also possible that the extreme temperatures of midday 

 may retard dehiscence. 



There are a few varieties which exhibit infertility in the field. Primus, 

 perhaps, is the most conspicuous of these. In Minnesota, in some years, 

 finely developed spikes may produce but three or four kernels. In the 

 West this variety is much more fertile. The cause of its infertility in 

 Minnesota has not been ascertained by the writers, since neither of them 

 has been at the St. Paul Station at flowering time since the pollen experi- 

 ments were developed. It may be that the anthers burst at inopportune 

 times or that many stamens may remain undeveloped. The senior 

 author found the latter condition to exist in the greenhouse in Wash- 

 ington. 



The experiments in keeping barley pollen did not lend any encour- 

 agement in this phase of the study. In practice, two suggestions may 

 be offered. Pollen can be kept several days by picking the spikes just 

 before the pollen matures and putting them in an ice box. The low tem- 

 perature will prevent further development for a time. When needed, 

 they can be placed with the stems in a glass of water in a warm room, 



