Some Anatomical Changes in the Cotyledonary Node in Relation to Correlative Inhibition of the Lateral Shoot Growth in Flax

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Abstract
Anatomical studies of flax (Linum usitatissimum variety Noralta) in relation to corrective inhibition of the cotyledonary shoots showed that the cotyledonary shoots contained proximally extending primary xylem strands, some of which were connected to the cotyledonary trace or axial bundles of the hypocotylary stele. At the bases of the cotyledonary shoots was primary xylem containing mostly tracheids. Secondary vascular strands containing short vessel elements, most of which were connected to the hypocotylary stele, especially after 72 h, were observed in decapitated plants. Cotyledonary shoot growth was similar for 72 h in decapitated plants and controls but thereafter increased exponentially in decapitated plants. The sequential effects of decapitation were an increase in cambial activity in the hypocotylary axis, the lateral spread of cambial activity into the primary bundles at the base of the cotyledonary shoot, the precocious differentiation of short perforate tracheary elements, the early establishment of a vessel bridge between the hypocotylary stele and the axillary shoot and the release of shoots from inhibition. Apparently the cotyledonary shoots show 2 phases of growth: limited growth of the shoot from inception until decapitation; exponential growth after decapitation which is depend development of the vessel bridge between the shoot base and the hypocotylary stele.