Cards with punched holes
There are two main types of access methods based around sets of cards (which can be reshuffled) with holes punched in them.
In the ‘species-per-card’ type, each card represents a species (or group of similar species), and holes around the margin represent different characteristics, perhaps ‘fleshy fruit”. If the species represented by the card does not make a fleshy fruit, the relevant hole is clipped, to make it into a notch. When a pin is passed in this position through a pile of cards and lifted, only the cards which represent species with fleshy fruits are left dangling on the pin.
In the other ‘character-per-card’ type a single master card has all the species in the guide written out at their specific point in a matrix and each punched card represents a character state, e.g. fleshy fruit. Holes are made in the middle of each card, at positions corresponding (on the master card) to all those species with fleshy fruits. By collecting together several cards for different character states applying to the specimen being identified, it is possible to see through the holes on the combined cards only those species that have that character combination.
Punched hole cards have been used in the past for certain types of plant identification guide with the species-per-card type more appealing for many field guides because species can be added as time goes by, and other notes or photographs about species can be added to the card.
Although these can be satisfying to use, like a game, especially with large sets of species, one problem is that each hole can only represent a yes/no. This is efficient for binary characters like ‘leaf lobed’, but less useful for multistate characters like flower colour, or smell. If these character states are to be usable for identification, separate holes are needed, e.g. flower blue (yes/no); flower white (yes/no). At least, then, it is possible for a single species to have more than one possible flower colour, but there is usually only a limited amount of space for characters.
Hence, species-per-card packs are best when the number of index characters is limited, and then some other method – possibly just browsing of the pictures of the species – is used for further refining the search within the selected set.
Alternatively, you could leave out the punched holes altogether. The Spades, Hearts, Clubs and Diamonds of classic playing cards can be seen as index icons, and you could design similar icons to represent leaf arrangement, for instance, with other details to separate species on each card. Such playing cards have been designed for games to stimulate interest in plant identification rather than for field guides per se. For field use, we would recommend some binding to prevent the pack becoming dispersed (See FRP R7367 Tree photoguide case study ).
Examples and references
Hyland and Whiffin's rain forest key has always been in dynamic format, moving with the times from a card index to computer programme.
Keay et al. (1964) appended to their Nigerian Trees field guide a ‘numerical key’ which, although usable in the static form in the book, was information in a format designed to be used in a reader’s home made card index.
Hansen & Rahn 1969
‘T Mannetje, L. 1966. A punch card key to species of Trifolium L. in Africa south of the Sahara excluding Ethiopia. E. Afr. Agric. For. J., 31: 261-270.