150 



The Journal of Heredity 



Another set of interesting adaptations 

 have been found in a type of maize 

 from the table-lands of Mexico. This 

 type was early recognized as a distinct 

 form. In 1829 it was given specific 

 rank by Bonafous under the name Zca 

 hirta. 



The most striking characteristic of 

 this type is a peculiar development of 

 hairs on the leaf sheaths and also to 

 some extent on the blades. For this 

 most conspicuous peculiarity we have 

 not as yet been able to discover any 

 adaptive significance. 



On the tablelands of Mexico where 

 this maize is grown the rainfall is very 

 light. In the parts of the United States 

 with a similar rainfall maize produc- 

 tiont is not considered possible. We 

 were, therefore, extremely optimistic re- 

 garding the utilization of this type of 

 maize. Our early experiments were very 

 disappointing. In the semiarid regions 

 of the West this variety was a com- 

 plete failure. Instead of being drought 

 resistant the plants appeared to suffer 

 from drought more than the ordinary 

 varieties from the corn belt. With- 

 out the viewpoint that each distinct 

 type of maize possesses adaptive char- 

 acters this variety would have been dis- 

 carded as worthless. As soon, how- 

 ever, as the variety was scrutinized with 

 respect to the separate characteristics 

 instead of trying to utilize it as it was, 

 important adaptations came to light. 

 The first peculiarity noticed was the 

 nature of the root distribution. In this 

 type of maize the roots seem to have 

 lost the ability to penetrate the soil. In 

 a full grown plant the roots are all hori- 

 zontal and confined to the upper 6 inches 

 of soil. There is so little direct attach- 

 ment to the soil that the whole plant 

 can be lifted up and down by the hand. 

 The plants are on rather than in the 

 ground. This peculiar root distribution 

 helps to explain why the plants are 

 able to grow in Mexico with so little 

 rainfall and why they fail in the western 

 part of our country. In the part of 

 Mexico from which this variety was 

 secured the little rain that falls comes 

 during the growing season in the form 

 of light, misty showers. The rainfall 

 is at no time suflicient to penetrate to 



any extent and an extensive superficial 

 root system is best adapted to utilize 

 the moisture. 



This particular adaptation we are un- 

 able to utilize in this country, for in 

 the drier parts of the United States the 

 rainfall comes largely in the winter in- 

 stead of during the growing season, and 

 growing plants must draw their water 

 from that stored in the ground some 

 distance below the surface. There are, 

 however, many regions in tropical 

 America where this adaptation should 

 be of vaKie. Through the work of 

 Briggs and Shantz, of the Department 

 of Agriculture, it has been shown also 

 that Zea hirta is the most economical of 

 water of any of the varieties of maize 

 yet studied. 



Still another adaptation possessed by 

 this type of maize was observed during 

 the past season in the course of experi- 

 ments conducted near San Diego, Cal. 

 It there developed that this type of 

 maize made satisfactory growth at lower 

 temperatures than any of the other 

 types with which we were experimenting. 

 This does not mean frost resistance, nor 

 does it mean that this type is suited 

 to extend maize growing farther north. 

 It means rather that this type pos- 

 sesses one of the characteristics neces- 

 sary to a variety of maize for regions 

 where the temperatures are uniformly 

 too low for the ordinary varieties. Tem- 

 peratures below the optimum for maize 

 are the rule over a large part of the 

 elevated regions of the tropics. In the 

 development of varieties for cool cli- 

 mates, this tyi^c of maize promises to 

 be of great value. Our experience with 

 Zea hirta shows also the folly of looking 

 for drought resistance as such. To 

 make progress, we must distinguish be- 

 tween the different kinds of drought re- 

 sistance and search for the particular 

 adaptation needed . 



Nearly e\'er>' region from which we 

 have received varieties has contributed 

 adaptations that ]iromise to be of value. 

 From Bolivia has come a type possess- 

 ing to a marked degree the quality of 

 remaining green for a long time after 

 maturity. Mexico has given us one 

 variety with the largest ears and another 

 with the abililN' to willistand extremely 



