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With Plate 7)the data from a total of some 3200 dissectionsb are involved, but nevertheless the sampling errors are in some cases unduly high. T h e method is laborious, l Of these, the first 1200 were carried out by Miss E. Bruck. to whom grateful acknowledgement is made, and the rest by P. B. Mathur. Am. BioL 31I ? '74 Studies in the physiology of the onion plant but without the information yielded by such dissections even an approximately correct picture of the plant's responses to external factors would seem to be unobtainable.Previous papers of this series (Heath, 1943 a, b) described a pfactor and a 5-factor experiment ( M a h Experiments, IWO-I) undertaken to give a wide preliminary survey of the responses of the onion plant to the external factors of temperature and day length, especially as regards the flowering behaviour, bulbing and ripening of onions grown from sets. They were concerned with externally visible re-the end of the usual storage period. Apart from this, the literature throws little light on the time relations of changes occurring at the growing point of the onion plant and none, so far as the present authors are aware, on the relations of these changes to external conditions. NORMAL DEVELOPXlL\i OF THE ONIOS PLAKTAn account of the general and histological development of the seedling is given by Hoffman (1933), the flower development described by Jones & EmswellerTABLE I. Main ewperiments, 1940-1. Treatments and symbols Factor Levels Symbols I. Timeofgermination 26. ii. 40 (10) hr. day) for F 8. iii. 40 (11) hr. day) forf } I II III IV V 2. Temp. in 1st season High (mean about 21°C.) F f 3. storage temp. TI Tt T. T ' T J T6 t, t, 18. iii. 40 (12 hr. day) for F 12. iv. 40 (13) hr. day) for F 6. v. 40 (15 hr. day) for F 2. v. 40 (15 hr. day) forf } 12. vi. 40 (16f hr. day) for F

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