4. Corn pollen size in varieties, hybrids and inbred lines.

The inbred lines are in two groups, those with 4 or less generations of selfing and one with more than 4 generations of selfing. Each group compared is based on 4 different stocks; one plant of each stock. One hundred normal pollen grains taken at random were measured for each plant; the 400 measurements for each group being averaged, the results are as follows:

Pollen sizes�S.E.

	Hybrids^1	Varieties	Inbred lines with
			more than 4 selfing	less than 4 selfing
	/1
Means	30.17�0.12	30.42�0.13	31.78�0.10	32.10�0.11
S. Dev.	2.34�0.08	2.53�0.09	2.01�0.07	2.24�0.08

Comparison and significance between

	Hybrids and:			Varieties and:
	Varieties	more than 4 selfing	less than 4 selfing	more than 4 selfing	less than 4 selfing	Inbred lines
Means	0.25�0.17	1.61�0.15	1.93�0.16	1.36�0.15	1.68�0.17	0.32�0.15
Dev.	1.4	10.7**	12.0**	8.6**	9.8**	2.1*
S.E.
S.Dev.	0.18�0.12	0.33�0.11	0.10�0.11	0.52�0.11	0.29�0.12	0.23�0.10
Diff.	1.4	3.0**	0.9	4.7**	2.4*	2.3*
S.E.

** Highly significant, 1% level of probability

* Significant, 5% level of probability

/1 Each unit = 3u

There are significant differences between pollen size of inbred lines and of varieties and hybrids; the pollen of the inbreds being the largest, the standard deviation of the variability of the inbreds being the smallest.

The following explanation is suggested: Since some qualitative genetic factors are expressed in the pollen, factors for quantitative characters may also be expressed. We expect that there would be a correlation between the expression of the genes in the sporophyte and in the gametophyte.

The variability of pollen grain size would be related to the degree of heterozygosis of the plant that produces the pollen.

The greater pollen size of inbred lines is considered to be the expression in the haploid gametophyte of the selection of the better balanced homozygous diploids. On this basis inbreds with longer inbreeding might be expected to be larger contrary to that observed. Further tests are being made of these relations and their importance in plant breeding and genetics.

Jose L. Blanco*

*This work was conducted with the collaboration of Doctor E. Vieitez, who made the taxonomic analysis.