F. O. Miles 213 



absence of one of these factors the phmt is pure white and soon dies, 

 while in the absence of the other factor the plant at first is yellowish- 

 white, but is capable of developing into a greenish condition and 

 sometimes into a pure gi-een plant. 



Studies of the relation between the other categories have not been 

 completed. Crosses of striped plants of the japonica type with golden 

 plants, and those of the green-striped plants with golden plants, and 

 also the crosses of green-striped plants with yellowish-white individuals 

 which turn green have all resulted in first generation plants which were 

 of the normal gi-een colour. Although it was impossible to note the 

 second generation plants, except during the first five weeks of their 

 growth, it was possible at that time to identify segregates of the 

 respective categories. The results secured in these crosses, however, 

 add further evidence to the hypothesis that more than one factor is 

 concerned in the production of normal green cohjur in the leaves of 

 maize. Apjjarently there is lacking in each parent some genetic 

 factor (or factors perhaps) which is concerned in the development 

 of chlorophyll, and, since the F^ plants are normal green, it appears 

 as if that facti.>r which is lacking in one parent may be present in 

 the other. 



In the pure white plants no plastids could be differentiated. In 

 the yellowish-white plants which later may become green plastids 

 apparently are present from the fii'st, although they are few in number 

 and are very small, gradually increasing in number and size as the leaf 

 turns green. 



In Zea japonica the manner of distribution of plastids may be 

 compared with the condition which Trelease (14) has described in 

 certain variegated Agaves. He found that the normal green condition 

 was due to the presence of plastids in the subepidermal region of the 

 leaf. In variegated leaves, if the stripe was pale greenish, there was 

 found to be a suppression of jalastids through several of the subepi- 

 dermal cells, while in a pure white stripe there was " all but complete 

 suppression of recognizable plastids." 



EXPLANATION OF PLATE. 



PLATE VIII. 

 Fig. 1. Pure white seedling. 

 Fig. 2. Ordinary green seedling. 



Fig. 3. Yellowish-white seedling 12 days after planting. 

 Figs. 4« and ib. Yellowish-white seedlings 15 days after planting. 



