Forensic Botany Lecture Notes PDF

16 PLANT ANATOMY IN FORENSIC INVESTIGATION Overview of plant anatomy  The study of the internal structure of plants is called plant anatomy.  Flowering plants consist of organized tissues composed of one or more cell types that are organized tissu...

16 PLANT ANATOMY IN FORENSIC INVESTIGATION Overview of plant anatomy  The study of the internal structure of plants is called plant anatomy.  Flowering plants consist of organized tissues composed of one or more cell types that are organized tissues. Each tissue consists of specialized cells organized in unique patterns.  They make up the leaves, flowers, stems, roots, fruits, and seeds that humans commonly use or consume as food.  When a stem, root, or leaf is dissected, the cells can be arranged in specific patterns that may be useful for classification and identification. For example, the internal arrangement of cells in the root structure of a dicot versus a monocot plant is characteristic.  The anatomy of plants can provide important forensic evidence by determining the part of the plant to which certain cells belong.  It is common in forensics to use various cells and tissues in identification of the plant fragment. The main plant tissue systems: 1- The Dermal System:  Includes epidermal cells, associated trichomes, and stomata.  Leaf epidermal features can be considered taxonomic for many plant species.  A case example: an expert witness was provided with crushed plant material and requested to confirm whether it was marijuana. The examiner selected the leaf fragments from the plant material. They are thin and contain numerous trichomes. He examined the cuticle in detail and compared the obtained results with the reference material, that is, Cannabis leaves kept in a herbarium. In effect, he rejected the thesis that marijuana was the plant material presented for analysis.  17 2- Ground system  Includes parenchyma, collenchyma, and sclerenchyma cells.  These cells have varying types, shapes, locations and perform numerous functions. 3- Vascular Tissue  Includes two conducting tissues: xylem and phloem. - Inclusions  Some cells may contain crystals of numerous sizes and shapes.  The pattern of their distribution and composition vary greatly from species to species. Clumps of raphides may be found in vacuoles within cells as in kiwi.  Many plants produce silicon dioxide inclusions called phytoliths which can be used for identification because they are characteristic of different species. When a plant dies, the phytoliths persist in the soil. Phytoliths also have been used successfully to compare soils and connect a suspect’s vehicle to a particular location.  Some plants may contain distinctive starch grains with characteristic shapes and composition and also can be used in plant identification. Types of plant materials used in forensics 1- Food plants  Edible fruits and seeds also can be useful forensic tools. Many fruits have special structures that stick to animals and in turn are transported by them to other locations. These same fruits may adhere to shoes or clothing of suspects and may link a suspect to a crime scene.  Furthermore, humans consume many fruits as well as intentional and inadvertent swallowing of seeds as part of their regular diets, and their identification in GI contents and feces may be of special forensic interest.  Plants within gastrointestinal tract, stomachs or feces can be identified by means of their anatomy. The contents can lead investigators to the place of a  18 last meal. Ingestion and partial digestion of a poisonous plant could also be determined.  Common Food Plants: Nearly, 3000 species of plants have been used as foods by human beings and that about 200 have been domesticated as food crops. Plant cells and time of death  Determining when a victim died is important in a homicide case as it indicates which suspects might be linked to commit the crime.  Because the pyloric sphincter muscle closes down upon death, any food remaining in  The stomach will provide clues to the last meal. Examination of stomach contents can be a useful method for determining time of death.  A full meal resides in the stomach for 2–6 h depending on a number of variables (Meal composition, Sex, Age, Body mass index).  Investigators can estimate time of death through information concerning the contents of the last known meal consumed by the victim (verified by witnesses, examination of the stomach or intestinal contents).  For example, if the victim’s last known meal contained corn, onions, lettuce, and tomato but the stomach contained green beans, potatoes, cabbage, and spinach, the victim must have consumed at least one additional meal before death. On the other hand, if the contents matched the last known meal, the window for time of death could be limited to a few hours.  Stomach or intestinal contents can be collected at autopsy. Also, Fresh fecal matter or vomitus collected at a crime scene or at autopsy. Then, samples are processed and prepared for microscopic examination and identification.  There are no good guides for anatomical identification of the plants we eat. A published work named The Structure and Composition of Foods Volume 2 focused on “vegetables, legumes, fruits”. Also, atlas of food plants that have useful anatomical features is available online.  19  It is useful to prepare yourself reference collection: The local grocery store is a great source for common food plants. These can be immersed in 70% ethanol and stored in tightly sealed containers. A set of permanent microscope slides also may be prepared for reference. 2- Wood  Wood from conifers (so-called softwoods) differs markedly in microscopic sections from those of dicot flowering trees (so-called hardwoods) because conifers lack vessels that are prominent in the dicot stems.  Different woods have their characteristic grain patterns formed by the xylem cells.  Since the wood of each tree species can vary somewhat in their grain patterns and, depending on how it is cut, it is often possible to connect broken or sawed pieces of wood or branches together (as in the famous Lindbergh case).  Fragments of wood are sometimes left at crime scenes and sometimes can be matched to their damaged source. Wood may appear in tissues of corpses at autopsy and can be examined microscopically with an aim to identify the source.  If wood is used as a weapon, the kind of plant from which the wood came can be identified by examining splinters or microscopic fragments and also by matching broken ends of the splinters or a damaged area to a tool mark. Tool marks made on wood can also be matched to a suspect’s tool.  When a saw is used to cut wood, the sawdust left in the teeth can be identified and matched. Sawdust left in a saw’s teeth can be valuable in cases of cutting high-priced timber. The importance of reference collections in microscopic analysis:  The fragmentary nature of most botanical trace evidence causes a challenge to the botanist in identifying the species of the trace evidence in question.  Typically, an experienced forensic botanist can identify fragmentary plant evidence based on trichomes (hairs), veins, or other surface features, but will  20 want to then compare that fragment to a more complete specimen of the species in a reference collection.  When the crime scene is known, the most important reference collection will be the collection of plants found at the crime scene.  Then the diagnostic minute or microscopic features of fragmentary trace evidence can be compared and possibly matched to those of the crime scene reference samples for positive identification.  The second important type of reference collection available to the forensic botanist is the herbarium.  Herbaria are archived collections of dried, preserved plants housed in many universities and natural history museums. Such collections are not specific to a crime scene; rather, they are generally built by the cumulative efforts of students and researchers at these institutions over the years to document the plants they have encountered during field work for research projects or class projects.  The ideal specimen has all the diagnostic features for a species, such as a portion of the shoot, flowers, or fruits, and comes with a label containing the identity of the species, the identity of the collector, and the exact location and date the plant was collected (found).  Herbaria at small universities include collections of a few thousand plant specimens of the local or regional flora, but herbaria at major institutions such as the New York Botanical Garden, Missouri Botanical Garden, and Kew Botanic Gardens house collections of several million specimens from many different parts of the world.  Herbaria allow the botanist to confirm identifications of trace evidence plant material, or even of unidentified reference samples collected from the crime scene.  21 Cases using evidence from stomach contents Case 1: Abusive Husband Gets the Axe  In 1996, a young German immigrant killed her abusive American husband with a borrowed double-headed axe after he had allegedly attacked her while she was asleep in her bed.  He allegedly had been abusing her since he had returned from the Gulf War in 1991.  She apparently laced his beer with Nytol ® and when he fell asleep, she hacked him more than 30 times with the axe while their three children were asleep.  The question was raised whether this was a consequence of the nighttime attack or was it premeditated since the axe was borrowed recently by the wife.  The examination of his stomach contents revealed the presence of corn and potato fragments as well as meat fragments from the meal she had served him for supper.  Furthermore, the muscle cells from the meat appeared quite fresh microscopically, suggesting the meat had been in the stomach for only a short time before his death.  This finding supported the prosecutions contention that he had been killed earlier in the evening and supported the conclusion that his murder had been premeditated.  However, the jury, believing the history of abuse was a mitigating circumstance, found her guilty only of second degree murder. Cases Using Evidence from Plant Anatomy Case 1: The Lindbergh case  the 1932 kidnapping and murder of the 20-month-old son of Charles and Anne Lindbergh that brought forensic plant science to the attention of the American public  Charles was a famous aviator and a national hero for being the first person to fly solo from the US to France.  22  The Lindbergh child was abducted from a second floor nursery by the use of a crudely constructed wooden ladder that was left at the scene.  Two years later, Bruno Hauptmann was arrested for the kidnapping after a portion of the ransom money was discovered in his possession.  Hauptman claimed that the money was left with him by a former associate and that he had no idea it was connected to the kidnapping.  However, a wood expert, Arthur Koehler, matched the grain in wood samples from Hauptmann’s attic to the wood of the ladder used in the abduction.  Kohler’s analysis confirmed the wood from the ladder was from Hauptmann’s attic and that tool marks found on the wood pieces matched marks left on test wood by Hauptmann’s tools.  He was convicted and sentenced to death in the electric chair.