WE do not always find it easy to classify the occupations of human beings : it is still less easy to do a similar job for all the plants known to us. The old joke about the man who gave as reason for his unemployment that he was a coronation-programme-scller embodies a principle that is not infrequently to be seen in operation in the plant-world. The chances of continuous occupation of any place at all may be few and far between for a very highly specialised organism. Our own species does not show anything like such great variation in equipment as do the various species of plants. We do not have men twenty feet high as window-cleaners nor
six inches high as needle-makers. Yet the range of size alone, in the plant kingdom, is very much greater than that. It is not surprising, therefore, that there is considerable difference of opinion among scientists concerning the best system for expressing our knowledge of the types of equipment possessed by living organisms and the uses made of them.
WHY THE BOTANIST CANNOT BE CONTENT WITH EVERYDAY WORDS THE term’life-form’ has been in common use among scientists to include such words as refer to the large-scale appearance or habit of a plant. Many of these words are in everyday use and are perfectly familiar : as tree, shrub, herb. These are very useful terms, but they are inadequate to deal with even our present knowledge. The simple words green or red may suffice for the traffic-policeman and the seaman : they will be inadequate for the haberdasher and the dye-manufacturer. As the latter practitioners need to distinguish a great number of shades of green, so the practitioner in the knowledge of plants needs to distinguish a large number of different kinds of woody or other plants. This approach to classification is a very old one—older than the attempt to classify according to relationship by descent. The early botanists used what we may call life-forms as the basis of their classifications. Nowadays most botanists would agree that Primus Cerasus and Fragaria chiloensis belong to the same family (Rosacea?); yet the first is the cherry, which can be a substantial tree, and the second is the strawberry, which is a lowly herb.
In order to understand some of the attempts which have been made and some of the difficulties of the subject it will be necessary to present an outline of one or two important systems of classifying life-forms. A simple one for land-plants is that of F. E. Clements :
I. 1. ANNUALS. 9. CARPET-HERBS.
II. 2. BIENNIALS. 10. SUCCULENTS.
III. HERBACEOUS IV. WOODY
3. SOD-CRASSES. 11. HALF-SHRUBS.
4. BUNCH-GRASSES. 12. BUSHES.
5. BUSH-HERBS. 13. SUCCULENTS.
6. CUSHION-HERBS. 14. SHRUBS.
7. MAT-HERBS. 15. TREES.
It should not be difficult for anyone to place any given land-plant in its appropriate class in this system. For many purposes it is adequate but the further the analysis is taken, the more elaborate becomes the system. Warming’s great work on the life-forms of plants takes account of seventeen great, of which seven are water-plants. The following account of the ten of land-plants is here given in as simple a form as possible :
ATMOPHYTES do not grow in soil but make use of atmospheric water by absorption over the whole of their exposed surfaces.
OMBROPHYTES also grow without soil but absorb water by means ofor similar organs or have means of storage.
CHYLOPI-IYTES are the plants capable of living among rocks or in similar places not porous enough to hold more than very scanty water-supplies.
HALOPIIYTES grow on salt soil where the water though plentiful is poorly available.
AGROPHYTES are theof ordinary well-watered soils with broad, not grass-like .
POIOIDS are the grasses and similar plants having long, narrow.
XYLOIDS include all plants with definitely woody.
KLINOPHYTES are the climbing and other plants which are unable to get into the light without support.
SAPROPHYTES are plants deriving their essential supplies from dead organisms.
PARASITES get their supplies from living organisms.
Each of these large groups is divisible into a large number of smaller units; for instance, the Agrophytes can be considered under some thirty or more minor divisions. It is not suggested that any non-professional person will find it necessary or desirable to pursue the analysis into such minute detail, but it is no bad thing to realize, if possible, that the complexity is presented to us by the organisms themselves. It is not a mere piece of learned perversity on the part of scientists.
Whether we use the high-sounding names or not, we must not, if we wish to understand the lives of plants, fail to recognise the units for which the words are, after all, a short means of reference only. We can agree that it is an affectation to speak of tonsorial artist when we mean barber or hairdresser, but that should not lead us to suppose that there are no
such people as those dealing almost exclusively with the hairy growths on the human head. When there is a simple term it is best to use it, but when the only simple word is inadequate or, worse still, is definitely misleading, it is time to get hold of another. It is doubtless a great mistake to fail to see the wood for the trees; but that must not blind us to the fact that a wood is composed of trees and a great many other things beside, or it would not be a wood at all. Purely professional terminology has been kept out of this account as much as possible, but it ought to be apparent that increase of understanding means increase of words if we are to communicate our knowledge.