132 Gates, Tetraplokl Mutants and Chromosome Mechanisms. 



In 0. gigas Sweden the amount of pollen produced is certainly 

 much in excess of that in the Palermo race, though there is no 

 evidence of a smaller percentage of bad grains in the meagre data 

 of Table V. It appears also, from Table VI, that there are more 

 3-lobed grains and fewer having 4 lobes than in gigas Italy. 



Turning now to the narrow-leaved yigas from the Amsterdam 

 cultures ( 180 / 12 )> I found no good grains at all, though the anthers 

 were fairly well filled with shrivelled grains, including several types 

 I had not previously seen. The 4-lobed grains appeared most 

 numerous, but their frequency, and that of the numerous 3-lobed 

 grains, was not determined. In both these types the size of the 

 lobes was large relative to that of the central part. In addition 

 a rounded, nearly spherical grain with very small lobes was observed, 

 but it appeared non-functional like the rest. The number of chro- 

 mosomes in this narrow-leaved individual has not yet been determined, 

 but I feel justified in" predicting that it will be less than 28. In 

 fact, I believe the most probable hypothesis regarding the cause 

 of the tremendous variation in leaf- width and other characters 

 exhibited by 0. c/igas is to be found in variations in the chromo- 

 some-number of different individuals. This will be brought about 

 by irregularities in meiosis, and the different types of individuals 

 in the offspring of O. gigas will thus represent a partial return to 

 the diploid number. It does not follow that all the size and shape 

 relationships in these plants are to be explained in this manner. 



In the flower of 0. Lamarckiana examined (Table V) the number 

 of good grains was found to be over fifty per cent., and the grains 

 were all, both good and ba*d, 3-lobed without exception. I after- 

 wards examined the pollen of several other flowers from different 

 individuals, but without counting the grains, but I found not a 

 single 4- or 5-lobed grain. I observed, however, that occasionally 

 two grains lie over each other in such a way as to appear like 

 one 4-lobed grain until carefully examined. Evidently 4-lobed grains 

 must be very rare if they ever occur in my strain of Lamarcldana. 



An individual of scwilata, which is a well-defined mutant type, 

 was examined. This plant (229. 1. 6) occurred in a culture of lata- 

 like plants from seeds kindly sent from Sweden by Nilsson 

 ("Komb. 1"). One very large 5-lobed grain was revealed in the 

 flower examined, but subsequent examination of another flower 

 without counting failed to disclose another such grain, though a 

 number of apparently 2-lobed grains were seen. A preliminary 

 chromosome count of this individual, from preparations made by 

 Miss N. Thomas, shows that the number is certainly as many as 

 fifteen, and possibly sixteen. This form will also be reported upon 

 more fully later, in connection with a paper on the various lata 

 forms. I may say that another scut il<i fa plant from de Vries' seeds 



