B - Pod corn: Has been obtained from two sources. "São Paulo Pod" and "Bolivia Pod". The latter was sent to us by Dr. Cardenas and later by Dr. Cutler. The other type came from one ear left casually in our department by a about which we know only that it came from São Carlos, that is from an inhabited and cultivated region only about 300 Km. from São Paulo and where we cannot expect to find "native Indian" corn. In all its characters, except of course being pod corn, it corresponds to the Brazilian corn of the region.

The studies of Bolivian pod corn are still in the beginning and we have met again the difficulties mentioned above, that corn from the Bolivian highlands grows well, but hardly produces ears in our altitude. Thus we can say only so far that it contains a dominant Tu gene.

São Paulo pod corn is also due to a dominant gene which is normally transmitted through the female while there is a strong selection against Tu-pollen tubes. At the most, half of them may eventually function, but generally less.

The original ear was large and well filled with a slender but very hard rachis. The seeds covered by large glumes, were small and more or less pointed and stood at the end of a long pedicel, of about the same length as the seed itself. The tassels of the first tunicate generation grown had drooping branches, with nearly normal or somewhat enlarged glumes and occasionally some silks.

Owing to the degeneration after inbreeding, the original line had to be outcrossed, and native Indian corn was used for this purpose.

The Tu ears in later generations varied very much, the extremes being silkless sterile ears, sterile ears with abnormally large glumes, ordinary fertile Tu ears and, finally, fertile ears with the kernels hardly covered by their glumes. The rachis remained always thin and rigid. In extremely large fertile ears the circumference necessary for the base of the kernels differed very much from the circumference of the rachis. In these cases the rachis split open lengthwise, the rows of grains remaining together in fours, with one group of two remaining when the total number was not a multiple of 4.

A successful selection was carried out to increase femaleness in the tassel. Finally a heavily bearded tassel was obtained with some 400 seeds and in its offspring the majority of all tunicate plants were again heavily bearded. In some cases it seems that each spikelet contained at least one female or perfect flower.

These hermaphroditic tassels were very large and drooping from the beginning. With the setting of seeds they became very heavy and tended to upset somewhat the balance of the plants. But one must not forget that a tassel with a total length of 40 cm. is small on a plant of over 3 m. There seems to occur in these tunicate plants an increase in the number of nodes between tassel base and ear, but the internodes remain short and the corresponding leaves show transformations in the direction of shucks.

However the most interesting transformations are to be found in the structure of the spikelets. The ordinary spikelets of the tassel with two male flowers are substituted, in different tassels, by a large variety of other combinations: 1 male or sterile and 1 female or perfect flower, 2 female ... 1 female and one perfect flower. But the most outstanding cases ... the spikelet of one tassel where one male flower was ... four female flowers. At the same time a tendency appeared for ... the ends of the individual silks into two arms, often of ... size. Thus the Tu gene causes the appearance of characters long ... in the group of the Maydeae and the related Andropogoneae: many flowered spikelets.

The observations reported above were mainly made on plants heterozygous for Tu. Owing to the elimination of the Tu pollen tubes, the number of Tu-Tu homozygotes must naturally be small. The phenotype of the homozygotes registered with certainty so far does not exceed the limits of variation of heterozygotes.

If we leave aside the effect of provoking the excessive development of glumes in the ear, then we may consider as next important feature in "São Paulo Pod" corn the accentuation of female tendencies in the tassel and the reappearance of characters lost in the phylogeny of many grasses: the re-establishment of hermaphroditism in individual flowers and the occurrence of spikelets with more than two flowers. But this does not necessarily mean that the immediate wild ancestors had these characteristics and may thus have belonged to another group of grasses, not the Maydeae or Andropogoneae. We may have to deal with still older characteristics of primitive grasses.

Recently Mangelsdorf and Reeves have modified the theory that pod corn with its covered grains in the ears is an approximation to the wild ancestor of maize, assuming that this ancestor was a plant without the lateral ears, but with covered seeds in the tassel. If this would be true, we should expect that the lateral branches, instead of having still normal, but sterile ears, should also terminate in some sort of bearded tassel. Selection in this direction has been started, but in order to obtain positive results it seemed necessary to substitute the modifiers of cultivated corn by modifiers of a "wild" form. This seemed possible only by crossing pod corn to teosinte.

F. G. Brieger

ss="para">F. G. Brieger

> had these characteristics and may thus have belonged to another group of grasses, not the Maydeae or Andropogoneae. We may have to deal with still older characteristics of primitive grasses.

Recently Mangelsdorf and Reeves have modified the theory that pod corn with its covered grains in the ears is an approximation to the wild ancestor of maize, assuming that this ancestor was a plant without the lateral ears, but with covered seeds in the tassel. If this would be true, we should expect that the lateral branches, instead of having still normal, but sterile ears, should also terminate in some sort of bearded tassel. Selection in this direction has been started, but in order to obtain positive results it seemed necessary to substitute the modifiers of cultivated corn by modifiers of a "wild" form. This seemed possible only by crossing pod corn to teosinte.

F. G. Brieger

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The original ear was large and well filled with a slender but very hard rachis. The seeds covered by large glumes, were small and more or less pointed and stood at the end of a long pedicel, of about the same length as the seed itself. The tassels of the first tunicate generation grown had drooping branches, with nearly normal or somewhat enlarged glumes and occasionally some silks.

 

Owing to the degeneration after inbreeding, the original line had to be outcrossed, and native Indian corn was used for this purpose.

 

The Tu ears in later generations varied very much, the extremes being silkless sterile ears, sterile ears with abnormally large glumes, ordinary fertile Tu ears and, finally, fertile ears with the kernels hardly covered by their glumes. The rachis remained always thin and rigid. In extremely large fertile ears the circumference necessary for the base of the kernels differed very much from the circumference of the rachis. In these cases the rachis split open lengthwise, the rows of grains remaining together in fours, with one group of two remaining when the total number was not a multiple of 4.

 

A successful selection was carried out to increase femaleness in the tassel. Finally a heavily bearded tassel was obtained with some 400 seeds and in its offspring the majority of all tunicate plants were again heavily bearded. In some cases it seems that each spikelet contained at least one female or perfect flower.

 

These hermaphroditic tassels were very large and drooping from the beginning. With the setting of seeds they became very heavy and tended to upset somewhat the balance of the plants. But one must not forget that a tassel with a total length of 40 cm. is small on a plant of over 3 m. There seems to occur in these tunicate plants an increase in the number of nodes between tassel base and ear, but the internodes remain short and the corresponding leaves show transformations in the direction of shucks.

 

However the most interesting transformations are to be found in the structure of the spikelets. The ordinary spikelets of the tassel with two male flowers are substituted, in different tassels, by a large variety of other combinations: 1 male or sterile and 1 female or perfect flower, 2 female ... 1 female and one perfect flower. But the most outstanding cases ... the spikelet of one tassel where one male flower was ... four female flowers. At the same time a tendency appeared for ... the ends of the individual silks into two arms, often of ... size. Thus the Tu gene causes the appearance of characters long ... in the group of the Maydeae and the related Andropogoneae: many flowered spikelets.

 

The observations reported above were mainly made on plants heterozygous for Tu. Owing to the elimination of the Tu pollen tubes, the number of Tu-Tu homozygotes must naturally be small. The phenotype of the homozygotes registered with certainty so far does not exceed the limits of variation of heterozygotes.

 

If we leave aside the effect of provoking the excessive development of glumes in the ear, then we may consider as next important feature in "So Paulo Pod" corn the accentuation of female tendencies in the tassel and the reappearance of characters lost in the phylogeny of many grasses: the re‑establishment of hermaphroditism in individual flowers and the occurrence of spikelets with more than two flowers. But this does not necessarily mean that the immediate wild ancestors had these characteristics and may thus have belonged to another group of grasses, not the Maydeae or Andropogoneae. We may have to deal with still older characteristics of primitive grasses.

 

Recently Mangelsdorf and Reeves have modified the theory that pod corn with its covered grains in the ears is an approximation to the wild ancestor of maize, assuming that this ancestor was a plant without the lateral ears, but with covered seeds in the tassel. If this would be true, we should expect that the lateral branches, instead of having still normal, but sterile ears, should also terminate in some sort of bearded tassel. Selection in this direction has been started, but in order to obtain positive results it seemed necessary to substitute the modifiers of cultivated corn by modifiers of a "wild" form. This seemed possible only by crossing pod corn to teosinte.

 

F. G. Brieger