Der Einfluß von Bormangel und von mechanischer Zerstörung des Spitzenmeristems auf die Zellteilung bei Sonnenblumen

Influence of boron deficiency and destruction of the apical meristem on the cell division in sunflowers With a severe, nearly absolute boron deficiency metabolism and formation of tissues are so disturbed that the primary symptom of boron deficiency can not be recognized with certainty. Investigations here had to clarify if cutting the tops or destruction of the apical meristem with a red‐hot needle will induce symptoms similar to those of boron deficiency or how symoms develop under mild boron deficiency. With the red‐hot needle technique, it was possible to obtain cambial enlargement in plants with a normal boron nutrition. Cutting off the tops also, induced an enlargement of the hypocotyl. In this case the enlargement was however due to an enlargement of the cortex by formation of an aerenchymlike tissue. A boron supply near the deficiency level caused development of deficiency symptoms in growing plants (chlorosis, inhibited enlargement of the stem, small deaf' blades, small‐celled xylem, malformed and discoloured cell walls and appositions on the young cell walls). As long as the shoot apex displayed growth, enlargement of the cabium did not appear as a rule. This symptom seems to be a secondary symptom of boron deficiency caused by damage to the shoot apex and, thus disturbed auxin metabolism.