228 BOTANY 



probably characters pertaining to haploicl ruhricalyx. It is 

 suggested that this haploid mutant developed parthenogenetically 

 from a ruhricalyx egg under the stimulus derived from the 

 foreign pollen tubes of eriensis. Other CEnothera haploids 

 have recently been described by Kulkarin and Davis and by 

 Emerson. 



Aneuploids. These are forms which have somewhat more or 

 less than the diploid number of chromosomes ; the number not 

 being an exact multiple of the basic haploid number. Aneuploids 

 as a general rule differ very much more from the normal diploid 

 form than do tetraploids, triploids, etc. Aneuploids with extra 

 chromosomes (hyperploids) are of common occurrence, but the 

 corresponding hypoploids are rare. The best known aneuploids 

 contain one more than the diploid number of chromosomes 

 (2n +1). These are called trisomies, and are best exemplified 

 by CEnothera lata, CE. scintillans. CE. ohlonga, etc., and by the 

 Datura mutants since investigated by Blakeslee and his associates. 



In Datura stramonium, which has been investigated by Blakeslee, 

 Belling and their co-workers, it w^as found that the haploid 

 number of chromosomes was 12. The make-up of these 12 chromo- 

 somes was as follows : one very large, four large, three large 

 medium, two small medium, one small and one very small. The 

 haploid mutants have one such set, normal diploids two, triploids 

 three and tetraploids four. In addition to these polyploids, a 

 considerable series have been discovered with the complement, 

 2n + 1. Other types have also been recorded, e.g., 2n + 1 +1, 

 2n +2, 4n + 1> and 4n — 1. The unbalancing effect of this 

 extra chromosome is shown in the so-called " globe " mutants. It 

 was found that the 2n + 2 globe has the characteristics of this 

 mutation more developed than the 2n + 1 mutant, and the same is 

 true of the 4n + 2 type compared with the 4n + 1 type. In each 

 case the degree of nuclear unbalance was reflected in the somatic 

 appearance of the plants. It was also found that the 2n + 1 

 mutants, both in Datura and CEnothera, differed in their external 

 appearance, as well as in their anatomical structure from the 

 diploid form. More recently Blakeslee and Belling have reported 

 the appearance of so-called " chromosomal chimeras," in which 



