8 BULLETIN 925, IT. S. DEPARTMENT OF AGRICULTURE. 



MORPHOLOGICAL SIGNIFICANCE. 



The recurrence of brachysm in maize is perhaps to be understood 

 from the normal presence of this characteristic in both staminate 

 and pistillate inflorescences. In cotton it appears as a lack of differ- 

 entiation between the floral parts and the internodes of the fruiting 

 branches, and not only are the internodes reduced but the floral bracts 

 are modified, becoming leaflike while the leaves become bractlike (4). 

 In maize, however, there is no indication of changes on the main 

 culm other than the shortened internodes, and the leaves are normal. 



The most striking example of brachysm in maize is the normal 

 pistillate inflorescence. Here a lateral branch has suffered so exten- 

 sive a reduction in the length of the internodes that even the 

 lower leaf sheaths of the branch inclose the terminal inflorescence. 

 In this respect the brachysm of the pistillate inflorescence resembles 

 that found in cotton, since the leaf blades have become much re- 

 duced or more frequently lost and only the sheath remains. This 

 is an approach to the floral condition where the glumes of the 

 spikelets are homologous with the leaf sheaths, and in this respect 

 the brachysm may be said to represent an intermediate condition 

 between floral and vegetative parts belonging to that class of varia- 

 tions designated by Cook (4) as metaphanic. This brachytic ten- 

 dency is usually confined to the branches from the upper nodes, 

 while those produced at nodes near but not necessarily below the 

 surface of the ground have internodes of normal length. In some 

 tropical varieties of maize the brachytic specialization of the upper 

 branches has been lost, and the result is a grotesque plant with one 

 or two ears borne at the ends of enormously lengthened ear stalks 

 which frequently exceed the main culm in height (PL VII). 



When accidents force into growth the branches below the ear, which 

 ordinarily remain dormant, they increase in length, or, in other words, 

 reduce in specialization, progressing toward the base of the plant. 

 The place where these branches change from having pistillate to 

 staminate terminal inflorescences is usually marked by a more com- 

 plete abortion of the buds, leaving an unbranched section of two or 

 three internodes. Thus the brachysm of the lateral branches is an 

 excellent illustration of a graded specialization, indicating gradual 

 development, but, although there are all stages of branch brachysm 

 on an individual plant, the advanced stages, as found on ear stalks, 

 are little affected by environment. 



Euchlaena, the nearest relative of maize, has no such specialization, 

 and, although all of the nodes except the uppermost produce a branch, 

 the apices of these branches are usually about the same height from 

 the ground. This results from the fact that in progressing toward the 

 apex of the plant each succeeding branch has one less node than the 



