Clearing can be successfully attained by soaking portions of leaves in a mixture of trichloroacetic acid and phenol (2:1) for 10–15 min at 60° C. These can be stained with writing ink (Chelpark make). The intensity of staining does not change even in permanent preparations. The preparations made as outlined above have been found specially beneficial for studying the morphology of fungi parasitic on leaves.

Calendula officinalis L. bears a short main axis and branches of several orders. The upper axillary branches grow vigorously whereas the lower branches remain arrested at different levels. Foliar application of gibberellic acid (GA₃) stimulated the elongation of the main shoot and of the upper few primary axillary branches (PAB’s). The length of the main axis nearly doubled 10 days after application. The endogenous level of GA₃ is probably sub-optimal, since external application enhances stem growth. However, treatment caused varying degrees of stimulation of the arrested branches. Whereas all the concentration of GA₃ were equally effective in promoting the growth of the first six primary axillary branches after 60 days of application, in plants treated with 500 ppm, the lower primary axillary branches failed to develop. Since the lower axillaries remained inhibited, it is presumed that 500 ppm of GA3 is supra-optimal. At 100 and 250 ppm, however, the growth of the arrested branches at the base was significantly increased.

Thirty days after application, GA₃ promoted growth and augmented the number of secondary axillary branches. Curiously at 100 ppm GA₃ markedly inhibited the length of the secondary axillary branches of PAB₃ to PAB₆.

These studies show that a complex mechanism of apical dominance operates inCalendula officinalis.

Apical application of cobalt chloride to female plants (50 or 100 μg/ plant) ofCannabis sativa caused drying of the shoot tip and formation of axillary branches. The latter bore male, reduced male and intersexual flowers, in addition to female flowers. Pollen in the flowers of altered sex were viable.

Separation of the outer bract enclosing the flower bud and spike axis results in the stimulation of amylase synthesis in the petals of gladiolus. Light is implicated in this process. Amylase production is localised in the petal epidermis (which is free of starch) and not generalised in the ground parenchyma (which contains abundant starch). Depletion of starch in the petal is strictly basipetal. It is proposed that the reducing sugars released from hydrolysis of starch in the ground parenchyma cause osmotic water intake, leading to petal expansion and flower opening.

The role of 10⁻² M, 2×10⁻² M, 4×10⁻² M potassium chloride, gibberellic acid (10⁻⁵ M; GA₃) and sucrose (5×10⁻² M) (used individually and in various combinations) in the elongation growth of excised ray-florets ofChrysanthemum morifolium var. Jyothsna, was investigated. KCl (10⁻³ M) caused 33·3% increase in elongation as compared to control (16·7%). With GA₃ and sucrose the percentage of elongation recorded was 39·8 and 28·9 respectively. Maximal growth response (82·8%) was recorded in KCl (4×10⁻² M)+GA₃ (10⁻⁵ M)+sucrose (5×10⁻² M). When used in combination either with GA₃ or sucrose, KCl showed an almost additive effect, whereas in the presence of both it acted synergistically. It is inferred that the increased turgor resulting from sucrose-promoted potassium uptake along with GA₃-caused tissue extensibility accounts for enhanced floret growth.

The percentage of buds opening and flower longevity as affected by the availability of water and sucrose to out spikes of gladiolus were studied. Uptake of sucrose solution and fresh weight changes in spikes were dependent on sucrose concentration. Marked reduction in uptake and fresh weight occurred when polyethylene glycol (peg) was used as the stressing agent. In comparison.peg failed to induce any significant change in the percentage of flower buds opening. Sucrose was essential for opening since the buds that failed to open in the control were caused to open in sucrose. Induced water stress did not curtail flower longevity at any given concentration of sucrose. Thus flower opening and longevity in gladiolus appear to be limited more by the availability of sucrose than water.

Flower growth and opening are commonplace events, but physiologically intricate and inadequately explained. In this review, we have brought together and evaluated information on this subject to focus attention on the dynamic facets of flower development. In particular, the physiological basis of flower bud dormancy, nature of cleistogamy, mechanism of flower bud growth and turgor maintenance and role of stamens in corolla growth have been examined. The regulation of flower movements and opening by temperature and light, and circadian rhythms in flower opening have been discussed, along with a consideration of the role of the petal epidermis in light perception.

It is emphasized that studies on flower physiology need to be intensified in view of the lacunae in our basic knowledge as well as to provide a sound basis for improving yields of both agricultural and horticultural crops.

Flower initiation is an important morphogenetic event. In this brief review the formative, ultrastructural, cytological and biochemical changes that occur in the transitional meristems in a few selected species have been discussed. In the evoked meristems, the number of plastids, mitochondria and ribosomes are usually higher. Further, an early shift of 4C nuclei to the 2C value, an increase in respiration and enhanced activities of dehydrogenase and phosphatase have been observed. The molecular events that ensue immediately after induction need further study.

The factors that regulate flower morphogenesis in vitro and reversal of excised flower buds to vegetative growth have been discussed. Reports on the modification of inflorescence development through the application of growth regulators have been analysed.

Changes in fresh and dry weight, content of sugars and starch and activities of α-amylase and acid invertase were determined during various stages of ray floret development and senescence inChrysanthemum. Total and reducing sugars increased until the ray florets attained their maximal expansion, peak fresh and dry weights. This coincided with the highest activity of invertase. Starch content and maximal activity of α-amylase declined much earlier. It is presumed that invertase rather than α-amylase plays a major role in the expansion of ray florets inChrysanthemum. Senescing stages of ray floret are characterized by decrease in fresh and dry weights and loss of metabolites and a marked decline in the activities of both invertase and α-amylase.