678 
Journcil of Agricultural Research 
Vol. XXVIII, No. 7 
Chromosome counts from pollen mother-cells of all species of Tripsacum 
studied are difficult and extremely so in all except T. dactyloides, where the reduc¬ 
tion phases are more regular. The author attributes this difficulty in determin¬ 
ing the chromosome number either to a lack of fusion of some chromosomes at 
diakinesis, giving nuclei that have more than 35 chromosomes, or to the com¬ 
bining of more than two chromosomes forming large chromosomes, giving nuclei 
with less than 35 chromosomes. The chromosome number, however, is too large 
to allow exact chromosome counts and classifications. Nevertheless a detailed 
study of pollen mother-cells of all the Tripsacum material available in the season 
of 1923 indicates that the haploid chromosome number is about 35. 
DISCUSSION 
The haploid chromosome number for representative species of the outstanding 
genera of the tribes of Tripsaceae (15) and Andropogoneae (8, 14, 15) have, 
with few exceptions, been found to be 10 and multiples of 10. 
Kuwada (18) has used the chromosome number found in a few Zea mays 
strains as a basic for his view that Zea is a tetraploid species derived from ances¬ 
tral types having 6 as the basic chromosome number. The author has made a 
preliminary investigation of the chromosome number in maize and maize rela¬ 
tives. He concludes, from the general occurrence of 10 and multiples of 10 
chromosomes in the four genera of the Tripsaceae and from the presence of 20 
haploid chromosomes in a recently discovered species, Euchlaena perennis, that 10 
is the basic chromosome number for Zea mays and its relatives. 
The outstanding species of this study has been Euchlaena perennis . The 
presence of 20 as the reduced chromosome number seems to attract attention 
toward the supposed close relation of the Euchlaenas and Zea. A chromosome 
number for perennial teosinte above that of the annual teosinte and maize makes 
the apparent relation among the three species difficult to explain. Morpho¬ 
logical characters indicate that the annual teosinte and maize are of more recent 
origin than E . perennis and that Tripsacum is the least specialized member of this 
group of grasses. Chromosome numbers of typical representatives of these 
three genera indicate that the more primitive and less specialized members have 
more chromosomes than the more recent and highly specialized species. 
The recent cytological studies in Rosa (8, 18, 28), Rubus (16), Oenothera 
(6), Datura (4), Triticum (21), Avina (11), Hyacinthus (17), and other poly¬ 
morphic genera seem in a general manner to indicate that the more primitive 
and more stable species have a smaller chromosome number , than more recent or 
hybrid forms. Such a conception must be reversed in order to derive Zea mays 
and Euchlaena mexicana from E . perennis or an E. perennis -like form having 
more than 10 haploid chromosomes, and to connect all these forms with the more 
primitive Tripsacums. 
A critical investigation of the above-mentioned cytological studies shows very 
few hybrids that have a chromosome number differing from the sum of the hap¬ 
loid chromosomes of its parents, and only one case, a haploid Datura (4), in 
which there was a chromosome number smaller than that of its parent. 
Rosenberg (20) utilized the occurrence of irregularities in chromosome distri¬ 
bution at meiosis to explain the increase in chromosome number of recently 
originated Crepis forms. This explanation generally applied to other genera 
should allow for an equal chance that hybrids will be found with a lower as fre¬ 
quently as with a higher chromosome number. 
F x hybrids between maize and perennial teosinte have 30 chromosomes and 
at meiosis show a chromosome behavior such as has been generally described for 
