F. R. Parnell 211 



Plate XXI shows photographs of whole anthers of the two parents 

 and F^. These were mounted in chloral hydrate solution containing 

 iodine, which shows up the pollen grains very well. Part of an F^ 

 anther is also shown more highly magnified, as also some free F-^ pollen 

 mounted in plain iodine solution. 



There can be no doubt that the two types recognizable in F^ pollen 

 represent the two ' genetic types produced by segregation. It thus 

 becomes possible to keep some track of segregation and to determine 

 the relative proportions of the two types of gamete in different plants, 

 flowers, anthers, etc. 



Examination shows that the two types occur mixed throughout all 

 parts of each pollen sac. Counts were made of the number of pollen 

 grains of each type in various anthers, the latter being teased out in a 

 drop of iodine solution in such a manner that every developed grain 

 could be distinguished. There was some variation in the proportions of 

 the two types and the ratio was rather more uniform for anthers in the 

 same flower than for anthers from different flowers of the same plant. 

 In eighteen anthers, from three plants, the starchy pollen varied from 

 43-2% to 51-87^, the average being 48-17^. 



An attempt was made to determine at what stage in spermato- 

 genesis segregation occurred. When this work was started the main 

 flowering was finished and only very poor material was available. It 

 appears, however, that there is little hope of success in this direction 

 owing to the absence of starch in the early stages. Pollen mother cells 

 in various stages of division were examined but no trace of starch could 

 be detected. The pollen grains themselves show no starch until they 

 are well developed and beginning to lay down reserve materials. 



A further examination will be made of better material from a crop 

 that is now being grown. It is hoped also, if time permits, to look for a 

 similar indication of segregation in oogenesis. 



A paper has recently been seen in which Bateson ' refers to the work 

 of Renner^ who detected dimorphism, due to genetic segregation, in the 

 pollen of Oenothera. The author has seen only a short abstract of this 

 work stating that the differences noted were in respect to size of pollen 

 grains and shape of their included starch grains. 



It is probable that a systematic search in other plants would reveal 

 many cases of similar dimorphism in pollen, e.g. in the form of starch, 



1 Bateson, W., " Genetic Segregation." American Naturalist, Vol. lv. No. 636, 

 January — February, 1921. 



- Renner, 0., Ber. Deutsch. Bot. Gcsell. Bd. xxxvii. (1919), No. 2, p. 129. 



