272 



THE AMERICAN NATURALIST 



[Vol. LV 



the older plant and Kuwada's figures and statements show that 

 maize is no exception to the general rule. This tendency for the 

 chromosomes in the radicle to be larger puts a fictitious value on 

 their measurements in this organ for comparison with the di- 

 mensions of chromosomes found elsewhere in the plant. As a 

 matter of fact, in the number of examples given the average 

 length of the chromosomes in all the plants is only a trifle more 

 than one per cent, shorter than the similar data in regard to 

 the chromosomes of the radicle, which ditference would not 

 greatly affect the end result. In this instance, although the 

 physiological location of the chromosomes was undoubtedly one 

 factor in determining their size, objection on this ground alone 

 to the submission of the records of the chromosome lengths in 

 substantiating the figure 172.17 as the fundamental chromosome 

 length for plant 58,,-,) would not seem to be entirely valid. 

 However, to base a broad conclusion on the lengths of the chro- 

 mosomes found in a particular part of a plant, even though com- 

 paring them with chromosomes from similar parts of other plants, 

 is likely to obscure the real condition. 



As has been shown in plant 58,,-,,. lengths of 172.17 mm. and 

 145 mm. were found. That these are not fixed lengths for the 

 particular tissues concerned in this variety of corn is shown by 

 the data given for other plants of the variety Black Mexican, in 

 which lengths vary (for corresponding tissues) from 132.5 mm, 

 to 181.25 mm., the average being 159.32 mm. There can be little 

 question that the variety Black Mexican, as long as it is genet- 

 ically pure, can have anything but comparal)l<' sets of i'lu-(Mn()- 

 some throughout, holding in mind that thouuli llir Ini-ths may 



tion in chromosome length is shown for the three phuits of the 

 variety " Sugar Corn " which were studied. The range of 

 averages here is from 147.8 mm. to 151.6 mm. 



Lastly, if real differences between the lengths of the chromo- 

 somes in plants 58,, and 22(,-,) exist greater differences be- 

 tween the members of the pairs that are found in the hybrid 

 offspring would be expected. Actually these elements mate 

 up well as to Icnirth and if unefpial homologous chromosomes have 

 enrored the zytrotes union in a common environment has regu- 

 lated tlif'ir i)fi)[)()rti(ins. As the diiiifiisions of the chromo- 

 9,(m\c> aiT in i)aft a ruiicfii>n of their environment the selection 

 as typical of any one comi>U'x or of even the average of com- 



