Observations by light microscopy of the process of exudation of nectar from the nectary hairs of Abutilon show that the nectar passes through the relatively impermeable cuticle in discrete droplets at regular intervals. From the observations it is concluded that there are pores through the cuticle at the hair tips which act as valves to produce these discrete drops. Numerous small pores at the expected positions are visible in electron micrographs.

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The flower of the trigger-plant Stylidium has stamens and style fused into a single column. A bend in the column, upon suitable stimulation by nectar-gathering insects, reverses its curvature in 10-30 ms, depending on species, causing the column to flip rapidly through an angle of 2-5 radians from its normal position against the anterior modified petal, the labellum, until it comes to rest against the posterior petals. This rapid movement or 'firing' provides a mechanism for cross-fertilization of the flowers. The column, after this rapid excursion then slowly resets to its original position in times from 200 to 700 s. Detailed measurements of the time courses of firing and resetting in several species of Stylidium have been made. During the firing, except for a short period of 1-10 ms in which it accelerates from rest under a force up to 50 g, the column moves with approximately constant angular velocity. This characteristic linear behaviour contrasts markedly with the distinctly non-linear time course of resetting. The dependence of firing and resetting rates on temperature has been investigated. A light-microscope study of the anatomy of the column shows that the mobile bend region possesses an internal anatomy strikingly different from the rest of the column. The bend consists of an inner core of three distinct longitudinal layers of thick-walled collenchymatous cells, surrounded by parenchymatous cells. A model in which changes in length pf the anatomically posterior outer layer of the core are greater than in the other layers is proposed to account for the movement of the column.

Analysis of Abutilon nectaries shows that the sugar content of the nectary rises sharply as nectar secretion begins. Nectar secretion on the plant occurs at a steady rate of 2-5 mg total sugar per flower. hour for 36-48 hr. A total of about 100 mg sugar per flower is secreted, and this is about seven times the maximum sugar content of the nectary at any time. Secretion of sugar in nectar by isolated nectaries floating on 0--0· 4M sucrose solution is in two phases. During phase I the rate is independent of concentration of sucrose in the external medium, but the rate is decreased by increasing the osmotic pressure of the medium with mannitol. In phase II the rate of secretion of sugar depends on the concentration of sucrose in the external medium and is independent of increase in osmotic pressure with mannitol. The rate is zero on water and reaches a maximum on about O· 4M sucrose. Secretion is reduced in both phases on media of sucrose concentration greater than o· 4M.By floating immature nectaries on sucrose solutions, secretion of nectar is induced earlier than would occur from nectaries on the plant.Respiratory inhibitors and anaerobic conditions reduce nectar secretion in both phases. Temperature has a marked effect on the rate of secretion, with a temperature coefficient (k20oc/klOoc) of 2·3.The total respiration of the nectaries was sufficient to supply only about one ~P per sugar molecule transported through an actively secreting nectary.The movement of the sugar component of nectar appears to be an active process (though influenced by water movement), but the mechanism is not understood.