4 ' ‘. 
336 LINDSTROM, GENETICAL RESEARCH WITH MAIZE 
noticeable by the distinct decrease in size, in texture or in color. In 
still others there is a complete abortion of endosperm leaving only the 
thin pericarp. In some the embryo is entirely lacking. There is another 
type with defective endosperm in which the primary root of the embryo 
begins growth on the ear before it is harvested. Such seeds die on ma- 
turing. 
Most, if not all, of the above noted types can be selected by 
continuous inbreeding so that they are remarkably uniform and are 
inherited as simple Mendelian recessives. Intercrosses of many of 
the types give normal grains in F, showing that they are genetically 
different. 
Another type of endosperm that is really defective is that called 
shrunken (Hutchison 1921). This too is a simple recessive to the normal. 
In this case the endosperm fails to develop completely, often leaving a 
hollow space near the center of the kernel. 
Still another endosperm defect has recently been reported as being 
conditioned by a recessive Mendelian factor. This type has been termed 
scar (sc) by Eyster (1922) because of its resemblance to a scar that 
forms on wounded tissue. | 
Plant characters. 
Numerous distinct, morphological variations of the maize .plant 
afford another source of genetic material. 
Dwarjness. — There are at least four different genetic factors con- 
trolling various forms of dwarfness in the corn plants. All are recessive 
to the ordinary tall habit of growth. The true dwarf type (d d) described 
by Emerson (1912) is easily detected in the seedling or mature plant 
stage. When mature the plants average about 30—40 cm. in height as 
compared with 2 meters or more in the normal type. The dwarf plants 
produce both staminate and pistillate inflorescences although both are 
inclined to be abnormal. In fact the plant is andromonoecious. 
The dwarfing is apparently due to a shortening of the internodal 
length, since the number of nodes (and number of leaves) is practically 
the same as that of a normal plant. 
Other types of dwarfs, such as the anther ear (an an) nana (na na), 
and brachytic (br br) have been reported. The anther ear type is also 
andromonoecious but is slightly taller than the true dwarf (d). The 
TCO pir ee 
