Morphogenetic properties of the parts of the colony of Clytia johnstoni

1. The morphogenetic potencies of the various parts of Clytia johnstoni have been ascertained by isolation and by grafting. 2. The various parts of the colony behave on isolation in the following ways: ( a ) Immediate development of a stolon (which in turn may grow hydranths, as in a normal colony). Shown by (i) all parts of the stolon except sometimes the growing tip, (ii) stalk primordia of length 0·5–1·4 mm, (iii) stalks of open hydranths (polarized, the stolon grows out of the cut basal end). ( b ) Immediate differentiation of a polyp. Shown by (i) stalk primordia longer than 1·7 mm and some between 1·4 and 1·7 mm, (ii) bulbs greater than 0·28 mm diameter (i.e. had reached contractile stage), (iii) bulb primordia of all sizes having a 'stalk' longer than 0·35 mm; only the larger bulbs became polyps if the 'stalk' was shorter than 0·35 mm. ( c ) Immediate incipient differentiation ( of a polyp? ) was shown by some stalk primordia of length 1·4–1·7 mm long. Partial hydranth differentiation (stomach and buccal region, no tentacles) was shown by an occasional isolated bulb. ( d ) Delayed stolon development. The time delay is variable but not random, with a marked tendency to start after 3–5 days and a less marked tendency after 9 days isolation. Shown by (i) all isolates which differentiated a polyp immediately on isolation, (ii) most bulb primordia less than 0·23 mm diameter and 'stalks' shorter than 0·35 mm, (iii) a few bulbs 0·23–0·27 mm in diameter. ( e ) No development at any time. Shown by (i) Stalk primordia less than 0·5 mm long, (ii) bulbs of less than 0·23 mm diameter, (iii) some stolon tips, (iv) most isolated polyps (after regression). 3. There is some evidence that a contractile growth region in an isolate gives it the power of immediate differentiation, in a stalk primordium to produce a stolon and in a bulb to a polyp. 4. The time at which a stalk primordium passes to a bulb primordium appears to correspond to the time when, on isolation, it switches from being stolon producing to being hydranth producing. 5. The peaks of regenerative activity (noted in 2( d ) above) are the same as the most likely life-spans of hydranths but it is not known if there is any relation between the two sets of observations. 6. The tips of growing stolons and hydranth stalk primordia have specific but weak inductive powers.