Anther calli of maize strains King Huang 13 and King Huang 9, Chun-Dan, Lai-Ping Bai, and Shu-Ke-chuang were employed. These calli grew about two months on N6 medium from the time of inoculation to the time of collection. Most of the collections and fixations were made at 3 o'clock in the afternoon. Materials fixed at this time were found to have the highest mitotic index. The fixative was acetoalcohol (1:3) and the squash was done in a drop of haemotoxylin.

When over 150 pieces of calli from the above five different maize strains were cytologically examined, it was observed that the frequency of the occurrence of mitotic divisions was very low. Only 178 dividing cells were found in these calli. The variations in chromosome numbers and their percent of the total were as follows:
 

	Chromosome No.
	5	6	7	8	9	10	15	16	19	20
No. cells	14	1	1	2	1	132	1	2	1	23
Percent	8	0.5	0.5	1	0.5	74	0.5	1	0.5	13

It is clear that most of the callus cells had 10 chromosomes. However, some of the cells had 20 chromosomes. Very few hypodiploid or hyperhaploid cells were observed. This relatively stable haploid condition might be accounted for by the fact that these calli were cultured only for a short period of time. It is known that long-term culture of plant tissue might produce more alterations in chromosome constitutions than short-term as reported by Torrey (1967). It can also be seen that the stability of chromosome constitutions varies among the calli of different maize strains. This observation is in agreement with that of Inomata et al. (1976), who found different chromosome stabilities in callus tissue of lines 3B54 and 3B58 of Chinese spring wheat (Triticum aestivum).

Y. C. Ting, Wan-chen Chen* and Chiao-sheng Hwang*

*Institute of Genetics, Academia Sinica, Beijing, China

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