STUDIES IN POLLEN, WITH SPECIAL REFERENCE TO LoNGEviTy 769 
was still capable of fertilization after one month. Germination grew pro- 
gressively weaker with increasing age. At 0° C., pollen remained viable 
for six weeks. Germination was better and pollen tubes grew longer 
than when stored at other temperatures. The pollen had not lost its 
germinative power after three months at —17° C. to —30° C. It may 
be concluded, therefore, that the lower the storage temperature, the longer 
Antirrhinum pollen remains viable. 
These experiments also show that the optimum sugar concentration 
for artificial germination varies from 10 to 30 per cent. 
Influence of carbon dioxide 
Since Kidd (1917) had found that high percentages of carbon dioxide 
in the atmosphere depressed the respiration of the seeds and therefore 
increased the period of longevity, some pollen-storage experiments were 
made under these conditions in 1917. Sealed glass tubes containing 15 
per cent of carbon dioxide were used as receptacles. 
The results, tho inconclusive, seemed to show that Antirrhinum pollen 
will remain viable longer in an atmosphere containing 15 per cent 
of carbon dioxide than in normal air. Similar conditions will result, 
however, whenever pollen is stored in containers merely sealed, for, due 
to respiration, the carbon dioxide content of the inclosed atmosphere 
will increase. 
In 1917, some pollen was stored in pure carbon dioxide. 
tubes were again used as containers. 
Sealed glass 
The results are given in table 13: 
TABLE 13. AntirrRHINUM PoLLEN StorED IN Pure Carson DioxiDE AT 
10°-20°C. 1917 
Pollinated Fertilized Germination Average length of pollen tubes 
Age In In In 
In air | carbon In air carbon In air carbon In air eae 
dioxide dioxide dioxide 
Days Number | Number | Number | Number | Per cent | Per cent 
Micemeee eeet alist 5 9 5 6 50 60 Shortase eee Medium-long 
Pile 12 15 10 9 20 60 Short-medium.| Medium 
DS ep cnet enanee evs TUG eal [rae e 11 60 40 Medium-long..| Medium 
42. 4 a 3 6 60 60 Medium-long..| Short—medium 
AGI PR Os cea\[Mors sravets ts Y Gtr ieee neeees AMAR Rene! si GOA ea eee Medium 
Goa ere cececs||| vcniw eye. LOM Ph oe eat (0) egal | rere Seta LONE | Notts rey tenes Short—medium 
BXs Une ciodeodl | aeeeteane Gres | a 20S 8). || oa ae Cay RII) SUS iets tater Peles ch Tine . Short-medium 
105. 8 4. 4 4 40 50 Medium...... Short-long 
PALE 6 8 6 F235. 2 I ar eA aT eae er Ene a oa BR Re Petde 
