﻿Hance : Pollen development in Zebrina pendula 67 



The cytoplasm becomes vacuolated and finally disappears entirely, 

 leaving the cracked and shriveled outer coat, Fig. 27. Many 

 anthers have been found filled with these empty coats. 



Somatic Mitosis 



A single drawing of the typical somatic mitosis has been 

 included with the others, Fig. 28. It can readily be seen that 

 the chromosomes are strikingly different from those figured in 

 the other drawings. 



Discussion 



The above work is of interest in comparing the development of 

 the pollen in normal seed producing plants with that of a plant 

 that has lost its power of setting seeds. It is impossible to say at 

 present whether or not the non-production of seeds is due to the 

 irregularities appearing in the chromosome behavior. Farmer 

 and Shove (2) consider that the varying number of chromosomes 

 in Tradescantia virginica may be due "possibly to the common 

 failure of the plant to set seeds." They, too, have recorded cases 

 of chromatic fragments and chromosomes being omitted from the 

 reformed nucleus and claim that they degenerate and are lost in 

 the cytoplasm. 



The question of synapsis will not be discussed here for, 

 although I am inclined to the view of parasynapsis from the 

 stages observed, the evidence is not sufficient as yet to base 

 definite conclusions on. Overton (9) gives an excellent bibli- 

 ography covering this question and the general field of cytology. 

 In Tradescantia and Galtonia, Mottier (8) holds that " there is in 

 many cells a marked tendency for some of the segments to adhere 

 end-to-end, forming chain-like rows of sausage or kidney-shaped 

 pieces." The peculiar conditions, however, existing in synapsis 

 and reduction in the heterotypic divisions of Zebrina pendula 

 suggest once more the question raised by Atkinson (i) as to 

 whether, among plants, there " are not different types of chromo- 

 some reduction," 



The lack of fusion between the individuals of the chromosome 

 pairs in the heterotypic division may point to a hybrid origin. 

 Gates (3) has cited conditions somewhat similar in hybrid Oeno- 



