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When one is more experienced with fungi it will be found necessary to carry out many microscopic observations, but when commencing the study it is necessary only to have an ordinary microscope; a calibrated eyepiece-micrometer is an advantage as is an oil-immersion lens. An examination of the spores is always necessary; the examination of features such as the sterile cells on the gill and stem, etc., varies with the fungus under observation. Spores should if at all possible be taken from a spore-print and mounted on a microscope slide, either in water or in a dilute aqueous solution of household ammonia. Although for mycologists it is often necessary to measure spores to within a ¹⁄₂ micron (µm) this book has been so arranged that one only really has to distinguish between a spore which is small (up to 5 µm), medium (5–10 µm), long (10–15 µm), or large if globose and very long (if over 15 µm); this is not strictly accurate, but serves the purpose for an introductory text. It is important to describe the character of the spore, i.e. ornamentations, whether a hole (germ-pore) is present at one end and/or a beak (apiculus) at the other (fig. 5). With white or pale coloured spores it is useful to stain either the spore or the surrounding liquid with a dye—10% cotton blue solution is admirable, or a solution of 1·5 g iodine in 100 ml of an aqueous mixture containing 5 g of potassium iodine and 100 g of chloral hydrate. Both these dyes must be accurately made up if the study of the fungi is to be taken at all seriously; because some of the chemicals used above are not normally required by students, a chemist must make up the reagents for you. Often the spores turn entirely or partially blue-black or pale blue or purplish red in the iodine solution—a useful character.

Larger illustration

Fig. 1. Dissection of a toadstool as recommended by the author. For explanation see text.

Material in good condition is always required and one of the first things the student needs to do is train himself to collect sufficient material in good condition. The steps by which all the structures of the fungus used in the text can be observed are outlined below:—

Fig. 1 shows the cuts required to furnish suitable sections in order to observe the various structures and patterns of tissue which are important.

1. Carefully place the longitudinal section (AB) of the fruit-body which has been sketched gill-face down under a low power or dissecting microscope. Hairs or gluten on the cap, if present, will be made visible by focusing up and down (figs. 2 and 3A) and/or those on the stem (fig. 3B). When any part of the cut fruit-body is not being examined retain it in a chamber containing damp paper or moist moss; this will assist the cells to retain their turgidity, for they frequently collapse on drying and are difficult to observe except after performing often lengthy and special techniques.

If only one fruit-body is available, then cut along CD and mount in a tin box on a slide in order to obtain a spore-print (otherwise see paragraph 6).

2. Cut off a complete gill (E) and quickly mount on a dry slide. Under the low power of a microscope, the cystidia on the gill-margin will be visible (fig. 4); it will be seen whether the spores are arranged in a particular pattern (fig. 5) and whether the basidia are 2-spored or 4-spored. In white-spored toadstools it is difficult sometimes to determine whether the basidia are 2- or 4-spored so one must confirm the observations by other techniques.

Larger illustration

A section of the gill accompanied by a small piece of cap-tissue, as in E, will confirm the presence or absence of noticeable cystidia (or hairs) on the cap. Now mount the section bounded by FG and HI in a drop of water containing either a drop of washing-up liquid and/or glycerine; the soapy liquid helps to expel any water which may tend to cling to the gill-margin amongst the cystidia and the glycerine stops the mount from drying out whilst further sections for comparison are cut and examined. It is at this time that the structure of the outermost layer of the cap can be examined, e.g. whether it is made up of a turf-like structure; the presence or absence of cystidia on the cap can be also confirmed (fig. 7A-C). It is frequently necessary to tap the mount in order to spread the tissue slightly and expose the elements; this can be done very efficiently by light pressure from the end of a pencil to which an eraser is attached. Cut off along line JK to eliminate marginal cystidia from confusing the picture and mount both pieces separately.

3. Cut out a wedge of tissue from the fruit-body (L) so as to have several gills attached to some cap-tissue; until one is familiar with the variability of facial and marginal cystidia, carefully cut along the line PQ (note: the cut is made one-third of the distance from the cap margin, thus eliminating the possibility of large numbers of marginal cystidia being examined in error for facial cystidia). Now make a second cut along the line of RS so that finally a small block of tissue remains (M).

Mount on a dry slide with the plane through PQ face down on the slide and observe under a low magnification, to assess whether cystidia on the gill-face are present or absent, and if present their general shape and whether numerous or infrequent (fig. 8).

Mount in water/washing-up mixture as outlined above and tap gently with the rubber attached to the end of a pencil; evenly distributed pressure should be given. If the gills appear to be too close then rotate the rubber a little whilst pressing in order to spread the tissue.

4. Using a low power of a microscope and looking down into the plane RS of the unmodified block M or a similar block, one obtains by this simple technique a very accurate idea as to the structure of the trama of the gill (fig. 9). The organisation of this tissue is very important in classification, some groups of toadstools having what has been described as regular trama (fig. 9C), others irregular (fig. 9D), inverse (fig. 9B) or divergent (fig. 9A). This same tissue may be thick or sparse to wanting, coloured or not. Such sections are often better than attempts at very thin sections unless very specialised techniques are used. There are few satisfactory thicknesses between the two extremes; the thick sections you can do and the very thin requiring expert techniques.

Larger illustration

5. Take out a small block of tissue T as indicated in the figure (fig. 1). Mount immediately and repeat as in 3. This will allow the outer layer of the cap to be more clearly seen (fig. 7A-C) and also the structure of the flesh (fig. 10). The latter may be composed of a mixture of filaments and ‘packets’ or ‘nests’ of rounded cells (i.e. heteromerous), or of filaments, only some of which may be inflated (i.e. homoiomerous); but when individual cells are swollen they never form distinct groups. By very similar techniques it is possible to show that the more woody fungi can have flesh composed of one of four types of cells (Corner, 1932): these types depend on whether distinctly thickened cells (plate 47) are present with the actively growing hyphae or not (pp. 140–150), whether hyphae are present which bind groups of hyphae together, etc. (plate 46).

6. Remove stem along line CD and cut out small blocks of tissue as indicated (U, V and W). Mount immediately and examine as in paragraph 3, for cystidia, etc. (see fig. 3).

Whilst all these sections are being cut and processed a second fruit-body, if available, should be set to drop spores; this is done by cutting off the cap from the stem and placing it either entirely or in part, and with gill-edges down, on a slide in a tin.

7. Z is a ‘scalp’ of a cap; a thin sliver from the cap is placed on a slide in a drop of water (modified with washing-up liquid, etc. as above). After placing a cover-slip over the tissue it is tapped gently; this will show if the cap is composed of globose to elliptic elements or if it is composed of strictly filamentous units (figs. 6A & B). Care must be taken not to reverse the section when transferring it to the mountant, either by turning the scalpel or by allowing the surface tension of the liquid to pull the section upside down. The construction of any veil fragments will also be seen in this mount, and if a loose covering of veil is present this should be removed before observation so that it does not obscure the fundamental structures.

8. Examine the stipe of the fruit-body used above under a low power or with a dissecting microscope in order to ascertain whether there are any remains of veil and/or vegetative mycelium. If found, mount immediately in the solution containing iodine mentioned above and examine.

Of course it is difficult to carry out the above system the first time and be successful in seeing everything, indeed in being able to cut all the sections 1–8. Practice makes perfect, so why not practise with a ¹⁄₄ lb of mushrooms from the grocer before the autumn season starts. In this way you will have overcome the difficulties without having to experiment with your collections.

CHARACTERISTICS FOR THE IDENTIFICATION OF HIGHER FUNGI WITH CAPS
Locality		G. Ref.		Date
Habitat notes	soil type	pH
vegetational community
solitary; in troops or rings
Draw or preferably paint exterior and vertical section of fruit-body
MACROSCOPIC CHARACTERS
CAP
	General characters:
diameter	shape	consistency
colour:	when immature	when mature
when wet	when dry
Surface
dry, moist, greasy, viscid, glutinous, peeling easily or not, smooth, matt, polished, irregularly roughened, downy, velvety, scaly, shaggy
Margin
regular, wavy	incurved or not
smooth, rough, furrowed	striate or not
Veil, if present
colour	abundance or scarcity
distribution at margin, whether appendiculate or dentate
consistency, whether filamentous, membranous
GILLS, or pores or teeth etc.
	remote, free, adnate, adnexed, emarginate, subdecurrent, decurrent
crowded or distant	distinctly formed or not
shape	interveined or not
easily separable from the cap-tissue or not
consistency (whether brittle, pliable, fleshy or waxy)
thickness	width
colour:	when immature	at maturity
number of different lengths or number of layers
obvious features of gill-edge, tube-edge, e.g. colour, consistency
STEM
	central, eccentric or lacking	shape
dimensions: length	thickness
hollow or not
colour:	when immature	when mature
consistency (whether fleshy, stringy, cartilaginous, leathery or woody)
surface characters (whether fibrillose, dry, viscid, scaly or smooth)
characters of stem-base
Veil, if present	characters
Volva, if present	characters
Ring, if present
whether single or double	whether membranous or filamentous
whether persistent, fugacious or mobile	whether thick or thin
whether apical, median or basal
FLESH
	colour in cap:	when wet	when dry
colour in stem:	when wet	when dry
colour changes if any when exposed to air
presence or absence of milk-like or coloured fluid
(note: colour when exuded on fruit-body immediately and after some time and when dabbed on to a clean cloth or paper handkerchief and exposed to the air).
SMELL	before and after cutting	—relate to a common every day odour
MICROSCOPIC CHARACTERS
BASIDIOSPORES
	colour in mass	colour under microscope.
shape	size	type of ornamentation, if any
size and shape of germ-pore, if present
iodine reaction of spore-mass:—blue-black to dark violet (amyloid); red-purple
(dextrinoid); yellow-brown or brown (non-amyloid)
BASIDIA	number of sterigmata
CAP-FLESH	type of constituent cells
GILL-TISSUE	type and arrangement of cells between adjacent hymenial faces
CAP-SURFACE	type of cells composing the outermost layer—whether filaments or rounded cells
STERILE CELLS—CYSTIDIA
	presence or absence of sterile cells:—
on gill-edge	on gill-margin
on cap	on stem
shape, estimation of size, thick or thin-walled, hyaline or not
types of ornamentation, etc.