A study was made of the effect of agar concentration on glassiness during meristem tip culture of carnation. Increasing the agar concentration from the usual 6 g/1 to 12 g/1 decreased glassiness, but at the same time reduced plant growth. A concentration of 8 or 10 g/1 reconciled these conflicting effects. The type of closure of the tubes was also found to affect glassiness, the looser types (cotton wool, metal caps, steri stops) being better than the tighter ones (aluminium foil and parafilm). In the first days after excision of the meristem tip a period existed in which a rather high temperature of 26 ~ favoured the development of normal plants later. The positive response to high temperature was around 3 days after excision.

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Stunt viroid can be detected in chrysanthemums with the polyacrylamide gelelectrophoresis (PAGE) method developed by Morris and Smith (1977) for potato spindle tuber viroid. The time of sample preparation can even be shortened considerably. The reliability of the short and the complete PAGE method proved to be similar to that of the biological 'Mistletoe' test in a parallel experiment. Combined samples can be tested in the complete PAGE method easily permitting the detection of one diseased chrysanthemum top in a total of ten.Although potato spindle tuber viroid is not known to occur in the Netherlands we searched for methods to detect possible infections. Artificial infections of tomato and potato plants and o f sprouts of potato tubers could readily be detected by Morris and Smith's method. Using this method it was possible to demonstrate infections by severe and weak isolates even when not yet producing symptoms. In tomato plants the viroid could be detected four to eight days before symptoms appeared.

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