Gates, Tetraploid Mutants and Chromosome Mechanisms. 



Lamarckiana would be regularly quadrangular with 4 lobes, while 

 triangular grains with an extra lobe would contain an intermediate 

 number of chromosomes. In making calculations based upon the 

 data given in my first paper on this phase of the subject (1909), 

 I find this idea strongly borne out. The figures in the following 

 Table are taken or deduced from the data given in that paper 

 (pp. 531, 533), the nuclei being treated as spheres. 



Table IV. 



From this table it can easily be calculated that, if the cyto- 

 plasm in gigcts pollen mother cells increased in the same ratio as 

 the nucleus, it should measure in volume 49244.67. The deficiency 

 in cytoplasm therefore amounts to about -23, or nearly one-quarter 

 of the amount of cytoplasm in the gigas pollen mother cell. While 

 these figures are of course only approximately accurate, yet they 

 make it at least reasonable to suppose that the fourth lobe in the 

 gigas pollen grain serves to restore the normal ratio between nucleus 

 and cytoplasm. 



Another simple calculation from the data given in my previous 

 paper (1909 a), shows that in 0. Lamarckiana pollen mother cells 

 in synapsis the ratio of cytoplasm to nucleus is about 24.58 : 1 , 

 while in 0. gigas the same ratio is only 16.83:1. 



With whatever degree of accuracy this relationship between 

 extra lobes and increased chromosome number may be found to 

 hold, it will be worth while keeping it in mind as a working hypo- 

 thesis. Miss Lutz (1909, p. 266) makes the statement that in 

 0. lata and (). Lamarckiana about one in a thousand grains have 

 four or more lobes, "although as high as fiften per cent, has been 

 observed in normal, typical individuals". The latter statement 

 requires verification. From the data presented in this paper, it is 

 evident that plants having different types of pollen grains differ 

 also in external characters and in chromosome number. It is 

 highly probable that the plants of Lamarckiana referred to by Miss 

 Lutz as having such a high percentage of quadrangular grains were 

 in reality triploid mutants. She mentions the frequent occurrence 

 of grains having 4 or more lobes in the triploid mutants described 

 in her recent paper (1911, p. 389), where she found the 3-lobed 



