Gates, Tetraploid Mutants and Chromosome Mechanisms. I > ] 



teristically 4-lobed, though grains with five and more lobes occur, 

 while that of the other forms is usually 3-lobed 27 ). 



The method used was to mount as much as possible of the 

 pollen from one anther at a time in a drop of water, and then 

 examine it and count the number of grains of the various types. Of 

 course, only a fraction of the whole number of grains in an anther 

 can be observed and recorded in this way, but by examining all 

 the pollen grains sufficiently isolated in a given field of the micro- 

 scope and then passing on to another field and examining all in 

 sight, one may be quite sure of obtaining the correct proportions 

 of the various types. In determining "good" and "bad" grains, 

 those were considered "bad" which showed any signs of shrivelling 

 or distortion, but probably the real proportion of non-viable grains 

 would be somewhat larger. When carried on in this way, the 

 examination of the pollen from a single flower requires a consider- 

 able time. Nevertheless, it is much more expeditious than cyto- 

 logical methods, and I believe it may prove a useful auxiliary 

 method in determining the nature of the different types of pollen 

 grains. 



It has apparently not occurred to Miss Lutz that the quadrangular 

 and triangular types of pollen grain may contain respectively 2 X 

 and X chromosomes, or thereabouts. If this were the case, a 

 critical statistical examination of the pollen in the various mutants 

 might greatly simplify the methods of determinig whether diploid 

 pollen grains occur, and their relative frequency in various parts 

 of the plant. This assumption is not at all an improbable one 

 when we recall the close association between the number of chromo- 

 somes and the size of the nucleus and the cell. I worked out these 

 relationships in some detail in the case of 0. gigas (Gates, 1909 a), 

 and have since suggested (Gates, 191 la, p. 926) that the 4 lobes 

 instead of 3 in the gigas pollen grain may result directly from the 

 changed space-relationships which follow the doubling in the chromo- 

 some number. The 4-lobed grain undoubtedly contains more space, 

 and therefore probably more cytoplasm, than 3-lobed grains, and 

 it is reasonable to suppose that its nucleus is therefore larger, not 

 only in gigas (as it undoubtedly is, though I have not made compara- 

 tive measurements of the nuclei in mature pollen grains) but wher- 

 ever 4-lobed grains occur. It is thus conceivable that the frequency 

 of 4-lobed grains in such forms as 0. Lamarckiana may be used 

 as a measure of the frequency of diploid pollen grains. I should 

 anticipate, however, that any diploid grains occurring in, e. g., 



27) In a previous paper (Gates, 1911 a, p. 926) I gave Miss Lutz the credit 

 for having first observed 4-lobed pollen grains, in O. gigas. But as a matter of 

 fact I myself observed and figured such grains (1907) in my first paper on this 

 subject, in a hybrid having twenty chromosomes. 



