芭蕉科花蜜腺形态比较：兼论其与传粉者的关系（英文）

对狭义芭蕉科3个属的代表性种芭蕉(Musa basjoo)、象腿蕉(Ensete glaucum)和地涌金莲(Musella lasiocarpa)的花蜜腺形态进行了比较研究。结果表明它们的蜜腺属于隔膜蜜腺。雌花的蜜腺着生于子房的上部,胚珠的上方;雄花蜜腺占据了整个败育子房的位置。蜜腺结构由许多腔道组成,这些腔道在横切面上呈现出复杂的发散式迷宫状结构。这3种植物花蜜腺的栅栏状表皮细胞、维管束和蜜腺开口方式相似,而从纵切面和横切面上观察其结构存在一些差异。PAS反应显示象腿蕉泌蜜组织中淀粉粒含量高于其他两个种;芭蕉和象腿蕉的蜜腺腔里有许多纤维状物质存在。3种植物的传粉综合征多样化,花序和花的特征(如花序下垂或直立、苞片的颜色、泌蜜量和泌蜜时间等)和传粉样式之间有密切关系。它们的蜜腺结构和传粉者行为之间没有明显的相关性,但是胶质或水质的花蜜对传粉者的取食方式有一定影响。     

荔枝花蜜腺的结构发育特点及其生物学意义

荔枝Litchi chinensis花蜜腺通过分泌蜜汁吸引传粉昆虫。蜜腺的结构和大小决定了蜜汁的数量和浓度, 后两者又必然影响昆虫的访花模式。本文研究了"糯米糍"和"妃子笑"荔枝花蜜腺的结构和发育特点。两个品种的雌、雄性功能花花蜜腺都位于杯状的花萼和具柄的子房之间及花丝周围的花托表面, 向上隆起, 形成发达突起的花盘蜜腺。成熟蜜腺结构上包含表皮、泌蜜组织和仅由韧皮部构成的维管组织, 属于典型的结构蜜腺。蜜腺表皮具多数发达角质化细胞壁的单细胞表皮毛, 表皮细胞外切向壁具厚的角质层。蜜腺顶端区具少数小的气孔器。泌蜜前, 泌蜜组织细胞具大量的淀粉, 且在泌蜜前后表现出动态的消长变化。泌蜜组织中具有两种不同形态特征的细胞分化, 推测其分别与蜜汁的合成和蜜腺组织损伤褐变的保护功能有关。雌、雄性功能花花蜜腺都是在花的其他结构基本分化完成后才开始分化发育的, 蜜腺的发育与大、小孢子的发育具有一定的协同性和相关性。依据蜜腺分化和发育过程的特征, 对荔枝花蜜腺在起源和系统发育上的特点进行了探讨。     

天南星科植物的花多样性与传粉策略

天南星科植物具有特殊的佛焰苞花序及多样化的传粉策略, 是研究被子植物花的分化与动植物之间进化生态学联系的理想材料。本文简述了天南星科不同类型的花序结构及其传粉适应意义, 总结了天南星科传粉策略的基本类型与演化历史。天南星科的苞片结构主要包括原始型、外展平面型、直立宽佛焰苞型和直立狭佛焰苞4种类型, 呈现出从简单的片状与外展平面状结构向复杂的立体包裹状的佛焰苞结构演化的趋势。肉穗花序可分为两性花花序、单性花雌雄同序和单性花雌雄异序3种类型, 演化路线为两性花花序→单性花雌雄同序→单性花雌雄异序。天南星科的传粉者主要有鞘翅目、双翅目、膜翅目昆虫, 表现出5种主要传粉策略: 食物报酬型互利传粉、气味吸引型欺骗性传粉、交配场所型互利传粉、产卵场所型互利传粉和致死陷阱型欺骗性传粉。天南星科植物通过花序的形状、颜色、产热以及花部挥发物来吸引传粉者, 其中最主要的挥发物有二甲基硫化物、甲基吲哚化合物、萜类和苯类化合物, 模拟食物或产卵场所信号吸引鞘翅目甲虫和双翅目昆虫为其传粉。天南星科植物的佛焰苞被认为是促进该科物种分化的一个重要结构, 但该性状的演化历史及其与传粉系统分化之间的内在联系尚不明确。利用现代分子生物学技术以及模型模拟等手段, 结合生理生态学方法深入探究传粉事件与天南星科植物的花多样性以及物种分化之间的联系, 有望提升关于植物-传粉者互作与植物的花多样性分化之间关系的认识, 并丰富对被子植物多样性演化相关研究的理解。     

国家二级保护植物翅果油树传粉生物学的初步研究

对翅果油树进行了传粉生物学的野外观察和实验表明：（1）翅果油树的花具有自花传粉的结构特征,同时具有蜜腺,又具备异花传粉的特征。传粉者主要是一种家养的蜜蜂。（2）翅果油树花形态结构与传粉者的形态和传粉行为非常协调和适应,昆虫的传粉部位主要是头前部和胸部。（3）蜜腺的产蜜量大,开花后1～2天蜜腺分泌量最大。对传粉昆虫竞争中具明显优势。昆虫的访花频率明显高于同花期的其他植物。（4）翅果油树没有融合生殖现象。     

四种蜜源植物花蜜腺的比较解剖学研究

草莓、漆树、芥菜和薄荷四种植物花蜜腺形态结构各异。草莓花蜜腺着生在花管内壁上属花被蜜腺。芥菜花蜜腺４枚,包括一对侧蜜腺和一对中蜜腺。漆树和薄荷的花蜜腺为花盘蜜腺,位于子房基部。四种花蜜腺都属结构蜜腺,其中仅芥菜的侧蜜腺组织中具维管束。它们在发育早期均无特殊的原始细胞,都由花器官表层细胞反分化形成原基,再发育成蜜腺。四种花蜜腺发育过程中细胞原生质体的液泡都表现出了规律性的消长变化。漆树和薄荷的花蜜腺具典型的淀粉动态变化,草莓的花蜜腺则属非淀粉型蜜腺;芥菜花蜜腺介于这两种类型之间。草莓和薄荷的花蜜由表皮细胞直接渗出。芥菜则气孔和表皮泌出兼备而漆树通过气孔泌蜜。     

草乌传粉过程中的广告效应与回报物质研究

虫媒传粉植物与其传粉者之间的相互作用被认为是被子植物花多样性的一个重要选择压力。这种相互作用体现在植物对传粉者的吸引以及传粉者行为对花粉的转运两个方面。本项研究通过去除不同的花部器官研究了草乌(Aconitum kusnezoffii)对其传粉者的吸引, 并结合传粉者的访问行为和草乌花的生物学特性探讨了传粉过程与交配系统的适应。红光熊蜂(Bombus ignites)是草乌的有效传粉者。去除花萼片显著降低了红光熊蜂的访问频率, 但去除特化成蜜腺叶的花瓣并没有显著改变红光熊蜂的访问频率, 这表明草乌吸引红光熊蜂的主要结构是由5枚萼片组成的花部外观形态, 而非花瓣。花蜜是草乌提供给红光熊蜂的回报物质, 糖浓度为39.23%, 组氨酸浓度为0.25 μg/μL。草乌花较大、单花花期长、雌雄异熟、花粉寿命长, 是一个自交亲和但需传粉者传粉完成繁殖过程的异交物种。草乌花序是无限花序, 当上部的花处于雄性阶段时, 下部的花正好处于雌性阶段。而红光熊蜂在草乌花序上的访问顺序通常自下而上, 带来异交花粉为下部的花进行异花授精, 同时又带走上部花的花粉, 这就很好地促进了草乌的异交。草乌雄蕊自外向内逐渐成熟, 是一种有效的限制传粉者单次访问浪费大量花粉的花粉装配策略, 能提高植物通过花粉散布获得的雄性适合度。     

垂柳花蜜腺的发育解剖学研究

垂柳雌花蜜腺一枚,位于于房与花序轴之间,多呈扁平广卵形,由分泌表皮、泌蜜组织和维管束组成。雄花蜜腺呈基部相连的两枚突起,一枚位于花丝与花序轴之间,基部宽扁,上部棒状;另一枚位于花丝与苞片之间,棒状,仅由分泌表皮和泌蜜组织组成。雌、雄花蜜腺均起源于花托表面2—3层细胞。在蜜腺发育过程中,雌、雄花蜜腺泌蜜组织细胞的液泡发生规律性变化．雌花蜜腺为淀粉型蜜腺,而雄花蜜腺为非淀粉型蜜腺。雌、雄花蜜腺的原宜汁分别由蜜腺维管束韧应部或花丝维管束韧皮部提供,其蜜计最后均由分泌表皮细胞和变态气孔排出。     

红姜花(姜科)同步大量开花的适应意义

两性花植物同步大量开花增加了个体花展示大小,能吸引更多的传粉者,使植株获得更多的交配机会,但也不可避免地带来不同程度的同株异花授粉,进而对被子植物的性资源分配、花部性状以及雌雄异株的进化等产生重要的影响.本文以姜科红姜花(Hedychium coccineum)为研究对象,通过人工授粉和操控试验、传粉动物的观察、自然结果率和自然居群的大小和密度的调查,探讨红姜花同步大量开花的适应意义.结果表明:(1)红姜花的穗状花序由57.33±1.68(n=30)个蝎尾状聚伞小花序组成,每个小花序具3.8±0.15(n=30)朵花,同花序上所有的小花序同步开花,不同小花序内的花按轮次同步开放,使花序在整个开花期间保持有数十朵花同时开放,花序水平上的花展示极为显著;(2)红姜花为自交亲和植物,但不存在自动自花授粉,自然居群存在严重的传粉者限制,其结实也存在着资源限制;(3)多型蓝凤蝶(Papilio memnon)、小矩翅粉蝶(Dercas lycorias)和黑角尖翅粉蝶云南亚种(Appias indra aristoxemus)是红姜花的有效传粉者,3种蝴蝶对红姜花不同大小花序的访问频率都显著不同,随着花序花展示大小的增加其访问频率也显著增加;(4)红姜花同一个体小花序内不同轮次花之间的胚珠数随轮次显著减少,而花粉数前3轮随轮次显著增加.胚珠数的递减及结实存在着资源限制,说明红姜花一个花序开大量的花并不是为了增加结实,而花粉数前3轮的递增,有利于花粉的分散输出,提高个体的雄性适合度.     

自交与异交象牙参属植物的蜜腺结构及其生物学意义

蜜腺是有花植物与传粉昆虫构建互惠关系的关键花部结构,解析不同繁殖特性物种间蜜腺结构的差异可为理解有花植物繁殖特性的演化提供理论依据。以传粉系统高度特化、异交实现有性生殖的早花象牙参（Roscoea cautleoides）和缺乏有效传粉者、主动自交实现有性生殖的无柄象牙参（R. schneideriana）为材料,通过野外测量2个物种蜜腺特性、超景深显微镜观察和石蜡切片染色,探究早花象牙参与无柄象牙参在蜜腺分布位置、外部形态及内部结构的异同。结果表明：2个物种均具有结构蜜腺,从外部形态来看,早花象牙参蜜腺体积较大、分泌糖浓度较高的花蜜,而无柄象牙参蜜腺体积较小、无花蜜分泌;从内部结构来看,早花象牙参蜜腺结构特化、各个组成部分有明显的区分,而无柄象牙参蜜腺出现一定程度的退化。该研究结果为揭示早花象牙参与无柄象牙参在花部特征、传粉机制及繁育系统的差异以及无柄象牙参蜜腺无花蜜分泌的可能机理提供了重要的形态学依据,也为深入地探讨植物与传粉动物间的协同进化关系以及理解蜜腺多样性的起源与维持机制奠定了科学基础。     

荠的花蜜腺发育解剖学研究

荠(Capsella brsa-pastoris(L.)Medic.)的花蜜腺共4枚,都呈半圆形、绿色。蜜腺由分泌表皮、泌蜜组织和维管束组成,属于结构蜜腺。在花的各部分分化后,由花托表层细胞恢复分裂能力形成蜜腺原基。在蜜腺发育过程中,泌蜜组织的液泡和淀粉粒发生有规律的变化。荠的花蜜腺按其着生位置,属于花托蜜腺;其发生方式属居间生长,4枚蜜腺同步发生;根据其结构和泌蜜前后的多糖物质变化分析,其原蜜汁源于维管束的韧皮部,通过泌蜜组织输送到气孔下腔,然后由变态气孔排出。     

Ultrastructure, Development and Secretion in the Nectary of Banana Flowers

The nectaries of Musa paradisiaca L. var. sapientum Kuntze werefound to secrete in addition to the sugar solution, a polysaccharidemucilage and a very electron dense, homogenous material whichwas apparently protein. The polysaccharide had already startedto appear outside the epithelial cells of the nectary at veryearly stages of nectary development. At somewhat later developmentalstages the very dense homogenous material appeared in the formof droplets between the plasmalemma and cell wall in massesin the nectary lumen. Nectar secretion started in flowers whenthe bract in the axil of which they occurred had just recoiled.The ER elements were dilated and formed vesicles and the Golgibodies were very active, at the stage of the nectar secretionand at stages preceding it, except at the stage just beforesecretion. In all stages of nectary development the dilatedER elements and most large Golgi vesicles contained fibrillarmaterial. It is suggested that both ER and the Golgi apparatusare involved in the secretion of the sugar solution and of thepolysaccharides. There was not enough evidence as to where inthe cell the very dense homogenous material is synthesized. A few developmental stages of the nectaries of the male flowersof the Dwarf Cavendish banana, which do not secrete nectar,were also studied. It was seen that at early stages of development,the ultra-structure of the nectary of this banana variety wassimilar to that of M. paradisiaca var. sapientum. However, theepithelial nectary cells of the Dwarf Cavendish banana disintegratedbefore maturation of the nectary. Musa paradisiaca L, banana, floral nectaries, ultrastructure     

The systematic significance of floral morphology,nectaries, and nectar concentration in epiphytic cacti of tribes Hylocereeae and Rhipsalideae (Cactaceae)

A long-standing interest in cactus taxonomy has existed since the Linnaean generation, but an appreciation of the reproductive biology of cacti started early in the 1900s. Numerous studies indicate that plant reproductive traits provide valuable systematic information. Despite the extensive reproductive versatility and specializations in breeding systems coupled with the striking floral shapes, the reproductive biology of the Cactaceae has been investigated in approximately 10% of its species. Hence, the systematic value of architectural design and organization of internal floral parts has remained virtually unexplored in the family. This study represents the most extensive survey of flower and nectary morphology in the Cactaceae focusing on tribes Hylocereeae and Rhipsalideae (subfamily Cactoideae). Our objectives were (1) to conduct comparative morphological analyses of flowers and floral nectaries and (2) to compare nectar solute concentration in these two tribes consisting of holo- and semi-epiphytic species. Flower morphology, nectary types, and sugar concentration of nectar have strong taxonomic implications at the tribal, generic and specific levels. Foremost, three types of nectaries were found, namely chamber nectary (with the open and diffuse subtypes), furrow nectary (including the holder nectary subtype), and annular nectary. All Hylocereeae species possess chamber nectaries, in which the nectarial tissue has both trichomes and stomata. The Rhipsalideae are distinguished by two kinds of floral nectaries: furrow and annular, both nectary types with stomata only. The annular nectary type characterizes the genus Rhipsalis. Nectar concentration is another significant taxonomic indicator separating the Hylocereeae and Rhipsalideae and establishing trends linked to nectar sugar concentration and amount of nectar production in relation to flower size. There is an inverse relationship between flower size and amount of nectar production in the smaller Rhipsalideae flowers, in which nectar concentration is more than two-fold higher despite the smaller volume of nectar produced when compared to the large Hylocereeae flowers. Variability of nectary morphology and nectar concentration was also evaluated as potential synapomorphic characters in recent phylogenies of these tribes. In conclusion, our data provide strong evidence of the systematic value of floral nectaries and nectar sugar concentration in the Cactaceae, particularly at different taxonomic levels in the Hylocereeae and Rhipsalideae.     

Comparative anatomy and morphology of nectar-producing Melastomataceae

Background and Aims

Most neotropical Melastomataceae have bee-pollinated flowers with poricidal anthers. However, nectar rewards are known to be produced in about 80 species in eight genera from four different tribes. These nectar-producing species are pollinated by both vertebrates and invertebrates.

Methods

The floral morphology and anatomy of 14 species was studied in six genera of nectar-producing Melastomataceae (Blakea, Brachyotum, Charianthus, Huilaea, Meriania and Miconia). Anatomical methods included scanning electron microscopy, and serial sections of paraffin-embedded flowers.

Key Results

All vertebrate-pollinated melastome flowers have petals that do not open completely at anthesis, thus forming a pseudo-tubular corolla, while closely related species that are bee pollinated have rotate or reflexed corollas. In most species, nectar secretion is related to stomatal or epidermal nectaries and not filament slits as previously reported. Moreover, the nectar is probably supplied by large vascular bundles near the release area. Blakea and Huilaea have nectary stomata located upon the dorsal anther connective appendages. Brachyotum also has nectary stomata on the anther connectives, but these are distributed lengthwise along most of the connective. Meriania may release nectar through the anther connective, but has additional nectary stomata on the inner walls of the hypanthium. Miconia has nectary stomata on the ovary apex. Charianthus nectaries were not found, but there is circumstantial evidence that nectar release occurs through the epidermis at the apex of the ovary and the lower portions of the inner wall of the hypanthium.

Conclusions

Nectar release in Melastomataceae is apparently related to nectary stomata and not filament slits. The presence of nectary stomata on stamens and on ovary apices in different lineages suggests that the acquisition of nectaries is a derived condition. Nectary location also supports a derived condition, because location is strongly consistent within each genus, but differs between genera.Key words: Blakea, Brachyotum, Charianthus, Huilaea, Meriania, Melastomataceae, Miconia, nectaries, nectary stomata, pollination     

Anatomy of the floral nectaries of some neotropical Salacioideae (Celastraceae)

Floral nectaries have contributed to the systematics of different taxonomic groups. Since those of the neotropical genera included in subfamily Salacioideae—Cheiloclinium Miers, Peritassa Miers, Salacia L. and Tontelea Aubl.—have different forms and positions, we explored their anatomy to delimit more precisely the genera of subfamily Salacioideae. Buds and open flowers of six species were treated following the usual techniques in plant anatomy. The obtained data were helpful in characterizing the floral nectary anatomy of the studied species. Furthermore, some features such as form, position and surface of nectaries; form of their epidermal cells; presence and distribution of stomata; occurrence of idioblasts containing druses in the nectariferous parenchyma; and absence of nectary vascularization can contribute to the taxonomy and phylogeny of the Salacioideae studied. In most of the studied species the nectar is probably released by both the stomata and the nectary epidermal surface. In Cheiloclinium cognatum, the structure acknowledged as nectary is actually a vestigial tissue and the functions of attracting and rewarding pollinators has phylogenetically migrated to the stigmatic region. The druses and phenolic substances observed in the nectariferous parenchyma probably help defend flowers against herbivore attacks. The minute size of the nectaries of Salacioideae may explain the absence of vascularization. The floral nectaries of Salacia elliptica are epithelial while those of the other species are mesenchymal.     

Floral Nectar, Nectary Structure and Pollinators in Some Argentinean Bromeliaceae

The floral nectar chemical composition and nectary structureof some Argentinean Bromeliaceae were studied, including fieldobservations on pollinators. Twenty species belonging to eightgenera from the three subfamilies were analysed. The nectarcomponents report is mostly new since no comprehensive studyhas been carried out on the family previously. Sugars were alwayspresent, while alkaloids, lipids, phenols, and proteins werenot detected in any sample. Reducing acids were found in threespecies. Amino acids were detected in a very low concentrationin only about half the samples. Pitcairnioideae species showa mean balanced disaccharide/monosaccharide nectar sugar composition,Bromelioideae had hexose-rich nectars and Tillandsioideae saccharose-dominantones. Nectar concentration ranged from 16 to 48 %. All taxabear septal nectaries with many common features. Pitcairnioideaeand Tillandsioideae members have half-inferior ovaries, a featuremostly overlooked in previous studies. Three types of nectaryarchitecture were recognized in both subfamilies. Bromelioideaehave inferior ovaries and possess comparable nectaries. Hummingbirdsconstitute the main flower pollinators of many species but butterfliesand bees were occasionally seen in two species, cropping nectarand pollen, respectively. Argentinean Bromeliaceae,, floral nectar, nectary structure, pollinators, alkalinity, abromeitiella, Aechmea, Bromelia, Deuterocohnia, Dyckia, puya, Tillandsia, vriesea     

Structure,ultrastructure and evolution of floral nectaries in the twinflower tribe Linnaeeae and related taxa (Caprifoliaceae)

Linnaeeae is a small tribe of Caprifoliaceae consisting of six genera and c. 20 species. In Linnaeeae, floral nectaries are located on the corolla‐filament‐tube and nectar is produced from unicellular glandular hairs. We studied 23 taxa using scanning electron microscopy (SEM), light microscopy (LM) and transmission electron microscopy (TEM) and found two distinct nectary morphologies, zonate and gibbous types, and two distinct types of glandular hair, clavate and smooth base types. Plesiomorphic characters associated with the nectary and identified in the tribe include hypocrateriform corollas, dichogamous flowers, zonate nectaries, wet papillate stigmas, vestigial nectary disc and smooth pollen grains. Apomorphic characters include bilabiate corollas, homogamous flowers, bulging nectaries, dry papillate stigmas and echinulate pollen grains. The nectary structure is similar in Vesalea and Linnaea and differs from the rest of the tribe, in accordance with recent phylogenetic results. Nectar secretion is typically granulocrine with subcuticular accumulation of nectar, which we compared with the secretion in multicellular hairs of Adoxa moschatellina. The cuticle on the hair becomes detached from the cell wall and large subcuticular spaces filled with nectar are formed. Nectar is probably released in areas with a thin cuticle. In Zabelia, the smooth basal part of the hair could help to build up the hydrostatic pressure.     

Nonsteroidal moulting hormone agonists: effects on protein synthesis and cuticle formation in Colorado potato beetle larvae

Adult parasitoid wasps can learn to recognize specific resource-based cues, making them adept at locating essential resources within their native habitats. However, relatively little is known about their ability to recognize the odors emitted by flowers and extra-floral nectar glands. A novel test arena mimicking the distribution of nectaries within an umbelliferous inflorescence was developed to measure and compare the responses of two eulophid wasps, Edovum puttleri and Pediobius foveolatus, to nectar-based odors. Although both parasitoid species were able to associate nectar location with the odors emitted by both real nectaries (dill flowers and snap bean stipules) and artificial nectars (1 M sucrose solution scented with banana or lemon food flavoring), the responses of inexperienced wasps to nectary odors differed. While inexperienced E. puttleri displayed little attraction to the odor of either dill flowers or snap bean stipules, inexperienced P. foveolatus displayed a strong attraction to odors of both types of nectaries. However, once it had experienced foraging on either dill or snap bean nectar, E. puttleri responded to those nectary odors as strongly as did P. foveolatus. The responsiveness of both wasp species to the odor of artificial nectar greatly increased after they foraged on sugar solution scented with either banana or lemon odor. That parasitoid wasp species can differ in their ability to recognize food-based cues is of fundamental and applied importance.     

NEC1, a novel gene, highly expressed in nectary tissue of Petunia hybrida

To study the molecular regulation of nectary development, we cloned NEC1, a gene predominantly expressed in the nectaries of Petunia hybrida, by using the differential display RT-PCR technique. The secondary structure of the putative NEC1 protein is reminiscent of a transmembrane protein, indicating that the protein is incorporated into the cell membrane or the cytoplast membrane. Immunolocalization revealed that NEC1 protein is present in the nectaries. Northern blot analyses showed that NEC1 is highly expressed in nectary tissue and weakly in the stamen. GUS expression driven by the NEC1 promoter revealed GUS activity in the outer nectary parenchyma cells, the upper part of the filament and the anther stomium. The same expression pattern was observed in Brassica napus. GUS expression was observed as blue spots on the surface of very young nectaries that do not secrete nectar and do accumulate starch. GUS expression was highest in open flowers in which active secretion of nectar and starch hydrolysis had taken place. Ectopic expression of NEC1 resulted in transgenic plants that displayed a phenotype with leaves having 3-4 times more phloem bundles in mid-veins than the wild-type Petunia. The possible role of NEC1 gene in sugar metabolism and nectar secretion is discussed.     

Erwinia amylovra Infection of Hawthorn Blossom: III. The Nectary

Abstract The nectaries of hawthorn flowers on detached branches were inoculated with Erwinia amylovora and the population development was followed by viable counts and light and electron microscopy. On nectaries bearing surface moisture at the time of inoculation ("wet nectary" material), the population increased rapidly after a short drop, or lag, lasting 6–12 h. Scanning electron microscopy showed that bacteria had multiplied within the nectarthodes during the first 6 h after inoculation, although, the total population had dropped. Death of cells on the surface of the nectary, possibly due to desiccation, may account for the overall drop. This differential response is not consistent with a bactericidal effect of the hawthorn nectary. On nectaries lacking surface moisture at the time of inoculation ("dry nectary" material), there was a 36 h lag period before the population started to increase – which coincided with the commencement of nectar production.
Although the nectary is an important site of infection during humid periods, the role of contaminated nectar in blossom-to-blossom spread of the disease is probably not of great importance.