The Aneuploids 357 



and seed coat. Cytological study of these trisomies is valuable for 

 determining the nature of chromosomal differentiation among specific 

 chromosomes.^^ 



Some fertile, partially stable i)lants can be derived by selling 

 inter-species trisomies instead of the tetraploid number or the extra 

 chromosome; morphologically distinguishable 54-chromosome lines 

 were produced. The interest in these types lies in their constitution 

 because the extra pair may be Irom an Asiatic-American wild or an 

 African species. This pair is added to the naturally occurring G. 

 hirsutum, a tetraploid 52-chromosome plant.^^ 



Another type, the intra-specics trisomies, arises from polyploids of 

 G. Jiiysutinn. By selling and appropriate crossing between various 

 trisomies in this class, both double trisomies and tetrasomics were 

 developed. 



There are then tAvo types of tetrasomics identifiable by the extra 

 pair, the intra-species tetrasomic and inter-species tetrasomic. As 

 the word suggests, the latter pair is derived from strains from another 

 species, whereas the intraspecific tetrasomics are limited to one 

 species.ii Morphologically both types may be distinguishable from 

 the species. A remarkable fertility is retained when a pair comes 

 from another species, but the intraspecific tetrasomics are almost com- 

 pletely sterile. A great many cytological problems can be solved with 

 these types. Trisomies and tetrasomics have been obtained in A^ 

 sylvestrus. Among the off-type plants from a progeny of monoploid 

 pollinated by diploid, trisomies were derived in wheat. Further self- 

 ing yielded tetrasomics. These added chromosomal types are not 

 easily detected in hexaploid wheat. Some homozygous speltoid wheat 

 proved to be 44-chromosomal plants. Tetrasomics and trisomies may 

 have been involved in the dwarf and subcompactoid types.-^^ 



7^.5— 2; Nullisomics and monosojnics. Chromosomes lost in dip- 

 loid plants do not survive. This was reviewed in an earlier section. 

 Tetraploids in Datura also lacking a chromosome or two failed to set 

 seed. Additions in diploids have been propagated extensively, but 

 these are often transmitted only through seed parents. 



At the polyploid level, missing chromosomes are tolerated.-" For 

 that reason some imj)ortant work can be done with two general types: 

 (1) monosomies, those plants lacking one chromosome, and (2) 

 nullisomics in which a pair is missing.^^i The latter are well known 

 among hexaploid wheat.^^ In Gossypium and Nicotiaua a success 

 similar to that for hexaploid wheat has not been achieved with nulli- 

 somics.^- 



Monosomic plants have been found in Gossypium spontaneously, 

 through nondisjunction in trisomies, and after intergeneric |)ollina- 

 tion.ii Since the transmission of haplo-deficient gametes fails in Gossyp- 

 ium. ihe further utilization of monosomies is stopped. In contrast 



