Gardeners' Chronicle, pp. 966-967 (Sept 12, 1868)
[The following paper was read before the British Association by Professor Karl Koch.]

Most botanists have only made use of the flowers and fruits of plants in the formation of genera; we have thus obtained, not natural, but artificial groups. For the formation of natural genera it is always necessary to know also the vegetation and the habit, both of which are very often in intimate connection with the flowers and fruits. This opinion I have at various times expressed in my works, and last in the preface of Ender's "Index Aroidearum." It is indeed necessary to study for a long time the plants of a family or of a genus in a living state, in order to discover the connection between the vegetation and flower. After having occupied myself more than 20 years with the study of the Aroideous plants, I am now in most cases enabled, when I have only a leaf, often only a piece of a leaf, of an unknown Aroideous plant, to divine also the construction of the flower and the fruit; and from the flower I know also the nature of the leaves; indeed, in few families of plants is the connection between the vegetation and the flower so great and so distinct as in the family of Aroideous plants. But I believe that in all families of plants there is a connection between the organs of vegetation and those of the flower, as may be well seen in the family of the Gramineous plants, where, for example, the species of the genus Poa and the group Poaceae are distinguished easily by the first leaves from the tribe of Festucaceae.

I have studied also for a long time the Crocuses and their vegetation. The flowers of these plants do not always furnish good characters; the proportionate length of the stamens and the style, on which botanists lay great value, is only relative, and is not always sure. Better characters for the great divisions are to be drawn from the vegetation. I have observed that many Crocuses twist the leaves spirally when they are dry. The same Crocuses have also a corm in which the scales or the sheaths are cut across transversely at the base. In this tribe of Crocuses are found blue, purple, white, and yellow flowers, as in the other tribes, where the leaves are straight, and so tenacious that they can be used as twine. The corms of the latter have here the scales minutely or strongly reticulated.

*In bot., to cut round in a circular manner,
as seed-vessels opening by a lid.

I will give, another example where the vegetation is of the greatest value for the systematist. Besides the leaves, the sheaths of the corms of the Crocuses are also very important. I distinguish by this means four groups; firstly, Crocuses with corms in which the scales are circumcissile* near the base; secondly, Crocuses where the scales are furnished with long and straight nerves; thirdly, Crocuses where the scales or sheaths are finely, or, fourthly, where they are strongly reticulated.

The bracts and the number of the flowers give also good marks for the distinction of the species; we have Crocuses with one and with two bracts, and with one or many flowers. I have taken the liberty to show here a collection of the more interesting species of Crocus. When I have finished my observations about the fruits and seeds, I hope to publish the treatise in extenso.

Finally, I would wish to draw attention to the advantage of photographs to the systematist for the comparison of plants. There are many plants of which the dry specimens in the herbarium are not sufficient, especially in the case of trees, where the best descriptions cannot give an idea of their physiognomy. The Liliaceous plants, and nearly all the Monocotyledons, in a dry state, give a bad view of their physiognomy. In our gardens and glasshouses such plants are cultivated which when photographed would give, more especially for monographers, good material for their description or their diagnosis. In our Botanic Garden at Berlin we are making now a collection of plant photographs, and I would beg possessors of gardens and greenhouses to communicate to me photographs of interesting plants and trees. I have the honour to show you a photograph of an Aroideous plant, which I owe to the kindness of Mr. Kolb, of the Botanic Garden at München. From this photograph alone I was able to determine that the plant was new, and from it I was enabled to make a good diagnosis and description.