376 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



ture and photoperiod. More effective, however, is the storage of 

 pollen from one season to another, for this has the advantage of 

 enabling the breeder to cross two varieties which are separated from 

 each other not only in time but also in space. With modern air 

 transport, pollen may be sent from one part of the world to another 

 in a very short time. 



Important though the question of the storage and viability of 

 pollen is, it has attracted proper attention only in recent years. 

 Under natural conditions most pollens remain viable for only a few 

 days or weeks, but this is not universal. The range of variation in 

 this respect may be illustrated by a few examples from common 

 plants. 2 InHordeum (Anthony and Harlan, 1920) and Oryza (Nagao 

 and Takano, 1938) fertilization cannot be secured with certainty 

 unless the pollen is transferred directly from the anther to the stigma. 

 In Sorghum (Stephens and Quinby, 1934) no seed could be obtained 

 when pollen was used 5 hours or more after collection from the 

 dehiscing anthers. In some experiments at Coimbatore 65 per cent 

 of the pollen grains of Gossypium were found to retain their viability 

 up to the twenty-fourth hour after collection but none after twice 

 this period (Banerji, 1929). At New Delhi the pollen of Solatium 

 melongena remains viable for only 1 day in summer and 2 to 3 days 

 in winter (Pal and Singh, 1943). At the other extreme, however, 

 is the pollen of Phoenix daciylifera, which is said to retain its viabil- 

 ity for a whole year 2a and which used to be an important article of 

 commerce in the past. 



Most pollens fall between the two extremes mentioned above, 

 but recent work shows that, whatever the viability might be under 

 natural conditions, it can almost always be prolonged to an appre- 

 ciable extent by storing the pollen under proper conditions. Hol- 

 man and Brubaker (1926), who have reviewed the older literature, 

 mention the extension of longevity of Cyclamen pollen from 18 to 

 185 days and that of Lister a ovata from 40 to 164 days. Samples 

 of Typha pollen which had been stored in a calcium chloride desic- 

 cator for 71, 94, 116, and 158 days, gave respectively 75, 70, 65, and 

 56 per cent germination, and 2 per cent of the pollen grains remained 



2 For further information on this topic see Maheshwari (1944). 



*" Stout (1924) contradicts this and says that he found no evidence of survival 

 of air-dry pollen for more than 77 daj^s, but as pointed out by Holman and Bru- 

 baker (1926), it is possible that under favorable conditions the period may be 

 much longer. 



