170 THE THEORY OF THE GENE 



ration division of the triploid, both in the pollen and in 

 the megaspore mother cell, there are 28 bivalents and 14 

 univalents. The latter pass to the poles at random. They 

 all divide at the second division. 



In the maples (Acer) there appears to be a possible 

 polyploid species. Taylor reported two species with 26 

 (n=13), two with 52 (n=26), and others with approxi- 

 mately 144 (n=72), or 108 (n=54), or 72 (n=36). Other 

 species with different numbers were also found. 



In the sugar cane (Saccharum) Tischler found races 

 with the haploid numbers 8, 16, and 24 (bivalent) chro- 

 mosomes. Bremer reports about 40 haploid chromosomes 

 in another variety and 56 in a third. Other numbers have 

 also been reported. Some of the combinations may be due 

 to hybridization, but little is known at present to what 

 extent the observed differences in number have arisen in 

 this wav. Bremer has also studied maturation divisions 

 of a few hybrids. 



In the genus Carex, Heilborn states that the chromo- 

 some numbers are quite different and that no apparent 

 polyploid series exists in this genus. "It is of importance 

 now to define somewhat more clearly the meaning of the 

 word polyploid. It appears from the list of chromosome 

 numbers in Chap. II that there are several numbers that 

 constitute, apparently, a series of multiples with 3 as the 

 fundamental number (9, 15, 24, 27, 33, 36, and 42), others, 

 again, that form a series with 4 as fundamental number 

 (16, 24, 28, 32, 36, 40, and 56), others with 7 (28, 35, 42, 

 and 56) and so on, but, according to the author's opinion, 

 these merely arithmetical relations cannot be regarded 

 as cases of polyploidy. The chromosome group of a poly- 

 ploid species must necessarily contain a certain number 

 of complete haploid chromosome sets and it must have 

 arisen through addition of such sets. We know, however, 

 that, for instance, C. pilulifera does not contain 3 sets of 



