Vernalization and Photoperiodism — 30 — A Symposium 



VARTi (1942). The following quotation applies to large samples, that for 

 small samples having already been described earlier ( 1938) . 



For these larger samples modifications were introduced, particularly in 

 regard to the containers of seeds and provision for absorption of COj from 

 the respiring seeds. The seeds to be chilled are first soaked under excess 

 of water to induce them to absorb about 60 per cent of their weight of water, 

 a procedure which generally requires 6 to 8 hours, according to the room 

 temperature. After removal of excess water by spreading the seeds over 

 several layers of absorbent cloth, they are placed in muslin bags or un- 

 glazed porcelain pots of suitable sizes and then placed inside the moist cham- 

 ber of the chilling cabinet. 



Any watertight box of required dimensions with removable lid can be 

 used for a moist-chamber. When boxes of thin wood are used, they should 

 be thoroughly asphalted inside and out. The inside of the box is lined 

 with blotting paper and sufficient water is placed at the bottom of the box 

 to maintain the absorbent lining moist throughout the period of chilling. 

 For absorption of CO,, a concentrated solution of potassium hydroxide is 

 kept at the bottom of the box in a large, flat porcelain dish, the rim of which 

 is previously paraffined to prevent creeping of KOH solution. A removable 

 thick wire-net frame is placed over the KOH dish to protect the seeds against 

 any accidental contact with the solution. Seeds in bags are suspended from 

 hooks screwed on to the removable lid of the box, care being taken to see 

 that the suspended bags do not touch the wire-net guard, or the moist 

 blotting-paper lining of the box. When unglazed porcelain pots are used 

 as seed containers, they are placed on the wire-net guard above the potash 

 solution. From daily readings of the maximum-minimum thermometer, 

 the temperature range to which the seeds are subjected is recorded. Ob- 

 viously, from these readings no definite idea is obtainable about the dura- 

 tion of the recorded temperatures each day. 



Sen and Chakravarti consider that an electrically operated cabinet 

 of the Frigidaire type with an automatic device for maintaining a constant 

 low temperature is undoubtedly the most suitable appliance for chilling 

 seeds, but having no available electrical supply were themselves obliged to 

 use a kerosene-operated Electrolux. An ordinary ice-box can be used, or 

 even a wide-mouthed thermos-flask when the temperature required is not 

 below 5°C. and only small samples of seeds are to be chilled. The thermos- 

 flask is half-filled with freezing mixture and the soaked seeds are hung in a 

 muslin bag from a hook screwed on the underside of the cork stopper of 

 the flask. The process of daily renewal of the freezing mixture ensures 

 the necessary removal of CO, and a supply of fresh air. Additional mois- 

 ture when required can be given to the seeds by dipping the bags in ice-cold 

 water ; the excess water automatically drips down into the flask. 



After the required periods of chilling, any mustard seeds which may 

 have sprouted are discarded and the unsplit seeds are washed and dried at 

 room temperature until they attain a constant weight. This period varies 

 in the United Provinces from 3 to 5 days, according to the season. The 

 seeds are then packed in a sealed container and stored inside an Electrolux. 



All five strains of mustard vernalized by Sen and Chakravarti re- 

 sponded to the treatment, the degree of response varying with variety. 



