CHROMOSOMES IN MAIZE AND MAIZE RELATIVES * 
By Albert E. Longley 
Assistant Cytologist, Office of Biophysical Investigations, Bureau of Plant Indus¬ 
try, United States Department of Agriculture 
An understanding of the laws of heredity is essential if improvement of plant 
breeding is to be controlled intelligently. A comprehensive understanding of 
the mechanism of inheritance demands definite knowledge of the chromosome 
number, not only of the forms it is desirous to improve but also of the related 
species. The present paper presents the results of a study of the chromosome 
number in several genera of the tribe Tripsaceae made in connection with genetic 
studies of Zea mays and its relatives. 
Very early in the investigation it was found that Euchlaena perennis had 20 
pairs of chromosomes instead of 10, the number found in annual teosinte, E. 
mexicana, and in maize. Since perennial teosinte hybridizes with maize and 
the cross seems likely to be of much genetic interest, it seems desirable to publish 
this fact together with other cytological data which have come to light. 
The larger part of the material used in this study was from plants growing 
during the summer of 1923 at Lanham, Md., Arlington, Va., and in one of the 
department greenhouses at Washington, D. C. The material for the study of 
the chromosomes of two Mexican Tripsacums was collected in Mexico by Messrs. 
Collins and Kempton the same season. 
Two cytological methods of investigation were used in the study of pollen 
mother-cell development. The iron-acetic-carmine method outlined by Belling 
( 1 ) 2 was used while growing material was available and it was found that very 
splendid mitotic figures were quickly stained and ready for study. To verify the 
results of this quick method, material was also killed in chromo-acetic or Bouin's 
solutions, embedded in paraffin, sectioned, and stained in Heidenhain's iron-alum 
haematoxylin. The former method is very satisfactory for studying chromo¬ 
somes, for they appear more normal than in material prepared by the second 
method, but the second method has the advantage of leaving permanent slides 
as records of the conditions found. 
EUCHLAENA 
Euchlaena perennis Hitch. Perennial teosinte. 
The material for a cytological study of the pollen mother-cell development of 
this species was taken from plants collected or from plants grown from seed col¬ 
lected in Mexico at the same time by Collins and Kempton (7). These plants 
were in one of the department greenhouses, Washington, D. C., and at Lanham, 
Md. The latter had been transplanted from the greenhouse in April. No dif¬ 
ference was apparent in materials from plants growing at these two localities. 
The haploid chromosome number in E. perennis was found to be 20 (PI. h 
A and B). Since this species is likely to become more important as it becomes 
better known by corn experimenters, great care was taken in determining the 
number and size of the chromosomes. The 20 bivalent chromosomes, as 
represented in Plate 1, C, are distributed in a regular manner during the hetero¬ 
typic division. 
1 Received for publication Apr. 9, 1924. 
2 Reference is made by number (italic) to “ Literature cited," pp. 680-681. 
Journal of Agricultural Research, 
Washington, D. C. 
( 673 ) 
Vol. XXVIII, No. 7 
May 17, 1924 
Key No. G-441 
