INTRODUCTION 27 
wool or hair of passing animals, and hooked seeds 
are found in Villarsia, hooked fruits in Bidens, 
Agrimony, Avens, Enchanter’s Nightshade, Carrot, 
Bedstraw, Woodruff, Sanicle, etc. In Burdock, 
after the burs catch in the wool, the plant returns to 
its position, jerking the seeds out. 
Plants have methods of expelling the seeds them- 
selves, as in Wood Sorrel, Touch-me-not Balsam, 
where the fruit is turgid in parts, and in Geranium 
there is a catapult motion owing to the valves 
curling up when dry. The Stork’s Bill buries its 
seeds deep in the earth. 
THE CLASSIFICATION OF PLANTS. 
The first attempt at classifying plants was based 
upon the obvious division of plants into groups 
depending upon habit, z.e. Trees, Shrubs, and 
Herbs. 
The old herbals which were medical botany for 
the most part were also very largely classified 
according to use of plants together with their 
habit. 
Later, in De Candolle’s classification, too much 
stress was laid upon the influence of function or the 
physiological characters of plants, as expressed in the 
terms ‘“ Exogens’”’ and ‘‘ Endogens,” which shows 
that a true classification of plants should be based, 
not upon externals, but upon morphological or struc- 
tural factors. None the less, in arriving at a natural 
