PHYSIOLOGICAL POLARITY AND DOMINANCE IN THE HOLDFAST SYSTEM OF CORYMORPHA

¹ HULL ZOÖLOGICAL LABORATORY, THE UNIVERSITY OF CHICAGO

1. The holdfasts of Corymorpha are tertiary axial gradients developing as buds from the secondary gradient of the basal region.

2. Their premature appearance and outgrowth in embryonic development under inhibiting conditions, as compared with their much later appearance and slower growth in development under normal conditions, suggest that a certain degree of physiological isolation from apical dominance is necessary for their development.

3. As the holdfast elongates, the cnosarc of its proximal region atrophies so that the distal portion becomes completely isolated from the parent stem, but advance of the tip continues until exhaustion occurs, the distal cnosarc remaining in good condition while atrophy continues at the proximal end. The delicate perisarcal tube secreted as the tip advances is the only connection with the stem in later stages.

4. Holdfast elongation is extremely rapid, sometimes 1 mm. in 15-20 minutes. After a few hours the rate of elongation decreases and exhaustion occurs after 2-3 days. The maximum lengths observed are 2-3 cm.

5. The holdfast tip in contact shows some amboid activity and while the earlier stages of elongation are apparently due largely or wholly to growth and may occur with the tip free in the water, the continued advance over the substratum after isolation from the stem and while undergoing decrease in size may be due in part to the amboid activity of the tip.