Wimmera ryegrass is a highly purified strain of Lolium rigidum, a 7-chromosome species native to the Mediterranean region. It is a spring annual that attains flowering without cold treatment. One would therefore not expect vernalization to have any effect on such a species.

J. P. Cooper (1954) found that when Wimmer ryegrass is sown outdoors in spring it will initiate flowering at the seventh to eighth node (mean 7.2). When it is sown in a heated greenhouse and given continuous light, considerable previously hidden variability is disclosed, and the seedlings initiate flowering at various nodes, ranging from the fourth to the twenty-first, as shown in Table V (mean node, 12.5). The variability will again be hidden if, before the continuous light treatment, the seeds are vernalized for six weeks at 3°C. When the cold treatment is followed by continuous light, the plants will initiate flowering at the fourth to the sixth node (mean 5.1).

TABLE V
Wimmera Ryegrass, Lolium rigidum, Latent Variability Revealed at Continuous Illumination (After Cooper, 1954)
 

	Node of floral initiation
	4-5	6-7	8-9	10-11	12-13	14-15	16-17	18-19	20-21	Total
Vernalization at 3°C	11	9								20
Heated greenhouse only	2		4	7	7	5	1	2	2	30

The cold treatment apparently starts and equalizes certain gene-controlled processes related to development. No previous selection has taken place for the combination of heated greenhouse and continuous light, and the plants accordingly reveal a considerable degree of residual variability under this artificial condition.

Cooper, JP. Studies on Growth and Development in Lolium: IV. Genetic Control of Heading Responses in Local Populations. Journal of Ecology, Vol. 42, No. 2 (Jul., 1954) , pp. 521-556