270 



THE AMEBIC AN NATURALIST [Vol. LV 



According to Kuwada there are two hypotheses concerning the 

 origin of Zea Mays L. litis (1911) first suggested that this mod- 

 ern form might have been derived from some unknown tribe of 

 Andropogonoa^ while Collins in 1912 put forward the claim that 

 Zea Mays L. was a hybrid between an unknown species of the 

 Andropogoneffi and EnchUcna. 



In his cytological studies Kuwada finds that in species of 

 Euchla na and A ndropogonea' the chromosome number is the same 

 as in Zea Mays L, — namely 20. In only one of the investigated 

 groups of plants belonginu- to the Andropogonea' was the chro- 

 mosome mimber above 20, which places this particnilar species 

 beyond consideration. The measurement of tlu' chromosoiues in 

 a Euchlana from south Florida shows that their total length is 

 greater than is the case in A ndropogon Nardus L. var. Georingin 

 Hack. The respective total c-hromosome lengths in each case are 

 given as 188.25 mm. and 111.3 mm. 



Kuwada gives the results of a large number of measurements 

 of the chromosomes in various varieties of maize taken at random 

 or from plants in which the cytological conditions have been 

 studied in the parental, Fj and F, generations. His conclusion 

 that the figures indicate that two length types of chromosomes 

 are concerned in the modern plant do not seem to the present 

 writer to be entirely born out by the facts. 



In the measurement of chromosomes previous studies have 

 shown that complexes from the same individual in the same or 

 in different parts of the structure may show considerable varia- 

 tion in the total length of their component chromosomes. In 

 general, of course, small cells will have smaller chromosomes and 

 larger cells, larger chromosomes, but even in similar tissues very 

 a])pr('('ial)le ditferonces may occur. These variations are ob- 

 vi(iiisl\- due l)(itli to internal and to 'external causes. Fluctuation 

 in tilt' rlinijiiic (If nutritive conditions may affect growth and 

 viuof, wliilr rlio volume of the cell imposes limitations on the size 

 of the contained chromosomes. It has been shown by the present 

 writer'' that, be the total length of a complex long or short, the 

 3Hance, R. T., 1917, "The Diploid Chromosome Complexes of the Pig 



