Apex size as an index of juvenility in ornamental perennials

研究了小苍兰和荷兰鸢尾对低温萌发的敏感性与其鳞茎和球茎质量、叶片数和先端大小等形态特征之间的关系，以确定其顶端分生组织从幼体到成体的过渡阶段。小苍兰球茎从休眠中释放出来后，其顶端逐渐变大，直径可达0.19-0.20 mm，这是其顶端分生组织由幼体向成体过渡的可靠指标，对低温具有较高的敏感性。小苍兰球茎上部芽尖大于基部芽尖，对低温的敏感性较高。这些数据表明，相变不是发生在单个植株上，而是发生在单个轴上。在荷兰鸢尾中，从幼年到成年的阶段变化不伴随任何形态变化。而在50-100ppm浓度的乙烯处理下，荷兰虹膜处理后立即发生了相变，增加了对低温的敏感性，但没有引起形态变化，说明荷兰虹膜在没有形态变化的情况下发生了生理相变。

Relationship between sensitivity to chilling for flower bud initiation in freesia and Dutch iris and their morphological characteristics, such as bulb and corm weight, leaf number and apex size, was investigated to identify the phasic transition from juvenile to adult in apical meristems.Apex of freesia corms enlarged gradually after releasing from dormancy and reached 0.19-0.20 mm in diameter, which is an reliable index of phasic transition from juvenile to adult in apical meristems, resulting in obtaining high sensitivity to chilling. Apex size of the upper buds on freesia corms was larger than that of basal ones and showed higher sensitivity to chilling. These data indicate that the phasic transition does not occur in individual plants but in individual axis.In Dutch iris, phasic change from juvenile to adult was not accompanied by any morphological change. While, application of ethylene to bulbs at the concentration of 50-100ppm promoted the phasic change immediately after the treatment and increase the sensitivity to chilling, though no morphological change was brought by the treatment with ethylene, indicating that physiological phasic change occurs without any morphological changes in Dutch iris.