Plant surface perception

Contact chemoreception of the dry plant surface is basically different from the well-studied perception of aqueous solutions. Since the stimulating compounds are in a dry state it may be that their distribution is not continuous and/or at a very low concentration. Thus not every contact between a sensillum tip and the plant would result in a stimulation. Although speculative, this may explain the specific behavior of various insect species after contacting plant leaves two female flies (P. rosae, D. brassicae) perform so called oviposition runs, on host leaves of about 20-30 s duration (Stadler, 1977,1978). Locusts make rapid vibrations (10-15 times per second) with the palps contacting the potential food plant surface. Blaney and Duckett (1975) showed that this palpation increases the amount of sensory input to the CNS by allowing disadap-tation of chemoreceptors between contacts. This must also be true for the tarsal hairs of two flies mentioned above. Some butterflies use the fore tarsi to drum or tap the plant surface prior to oviposition (Ma and Schoonhoven, 1973 ... 

Materials science associated with fracture mechanics has mainly been confined to composite materials such as concrete, ceramics and metals. Much of the emphasis of the research has been on preventing fatigue and failure rather than designing for it to occur. The way a structure deforms and breaks under stress is crucial for properties such as flow and fracture behaviour, sensory perception of structure, water release and the mobility and release of active compounds. In the case of foods, the ability to break down and interact with the mouth surfaces provides texture and taste attributes. The crack propagation in a complex supramolecular structure is highly dependent on the continuous matrix, interfacial properties and defects and the heterogeneity of the structure. Previous structure-fracture work has dealt with cellular plant foods, and it has been demonstrated that the fracture path differs between fresh and boiled carrots due to cellular adhesion and cell wall strength as well as cell wall porosity and fluid transport (Thiel and Donald 1998 Stoke and Donald 2000 Lillford 2000). 

The thalamus functions as a relay station for sensory and motor information going to and from the cortex to other areas of the brain and body. The outermost layer of the brain is the cortex, which is made up of layers of nerve cells or neurons, and has a highly folded organization that increases its surface area and the number of neiuons that it contains (11, 17). The cortex is involved in many aspects of psychotropic plant use, from the primary effects of psychoactive drugs on sensations and perceptions, to the complex behaviours and thoughts involved in drug craving and uncontrolled use (17). 

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