3 Examining specimens with a microscope
Some fungal spores can be examined suspended in just water, but others require the use of a staining agent such as Melzer’s solution. This solution contains various chemicals including iodine, which reacts with starch to produce a blue-black colour and shows up the surface characteristics of the spores.
To examine a sample, place a glass slide with a coverslip on the stage of the microscope. Start off by using a relatively low-powered objective lens to focus the image and scan around for suitable spores or other material to examine. Once you’ve selected an area to examine in more detail, switch to using a high-powered lens. (Note: it is particularly important to be careful when focusing high-powered lenses as the depth of focus is tiny and it is very easy to crush the slide by accidentally turning the focusing knob in the wrong direction.)
The size of objects can be measured using an eyepiece graticule, which superimposes a scale on the image. Size is often a very important diagnostic factor in fungal species identification.
Activity 1 Examining specimens with a smartphone
Using a smartphone camera, take a photo of a coin, getting as close as you can and using the highest resolution possible. Then zoom in on the resulting image as far as you can. Are there details shown in the image that you are unable to see with the unaided eye? What limits the amount of detail seen?
Answer
Some coins, such as UK coins, feature very small letters (e.g. below the monarch’s head) or other details that are difficult to read with the unaided eye but may be more visible when examining an image taken with a smartphone. However, the amount of such detail may be limited if you were unable to keep the phone perfectly still when taking the image or if there was a very limited depth of field.
These factors may be very important in the field when trying to use a smartphone to obtain close-up images of mosses or insects. So always take plenty of photos to be sure that you have at least one that is correctly in focus and sharp. Some phone cameras have special modes that take lots of pictures and select only the ones that are sharp. They may even stack the images together by selecting just the in-focus parts of several images and combining these to give an image with increased depth of field. This function can be very useful for analysing small objects, but if you use it be sure to watch out for artefacts creeping in, such as an insect having extra hairs or legs!