430 BIOGRAPHICAL SKETCHES. 
conclusions in respect to the fundamental unity, and therefore 
common source, of vegetable and animal life, grew out of an 
observation which the author made in the summer of 1860, 
when he “ was surprised by finding how large a number of 
insects were caught by the leaves of the common Sun-dew 
(Drosera rotundifolia), on a heath in Sussex.” Almost 
everybody had noticed this; and one German botanist (Roth), 
just a hundred years ago, had observed and described the 
movement of the leaf in consequence of the capture. But 
nothing came of it, or of what had been as long known of our 
Dionzea, beyond a vague wonderment, until Mr. Darwin took 
up the subject for experimental investigation. The precursor 
of his volume on “ The Movements and Habits of Climbing 
Plants,” published in 1875, as well as of the recent and larger 
volume on “ The Power of Movement in Plants,’’ 1880, was 
an essay published in the “ Journal of the Linnean Society ” 
in 1865; and this was instigated by an accidental but capital 
observation made by a correspondent, in whose hands it was 
sterile; but it became wonderfully fertile when touched by 
Darwin’s genius.! His latest volume, on “ The Formation of 
Vegetable Mould through the Action of Worms,” is a devel- 
opment, after long years, of a paper which he read before the 
Geological Society of London in 1837. 
These subsidiary volumes are less widely known than those 
1 Mr. Darwin’s quickness in divining the meaning of seemingly unim- 
portant things is illustrated in his study of Dionea. Noting that the 
trap upon irritation closes at first imperfectly, leaving some room within 
and a series of small interstices between the crossed spines, but after a 
time, if there is prey within, shuts down close, he at once inferred that 
this was a provision for allowing small insects to escape, and for retaining 
only those large enough to make the long process of digestion remunera- 
tive. To test the surmise, he asked a correspondent to visit the habitat 
of Dionza at the proper season, and to ascertain by the examination of a 
large number of the traps in action whether any below a certain consider- 
able size were to be found in them. The result confirmed the inference, 
a comparatively trivial but characteristic illustration of Darwin’s confi- 
dence in the principle of utility, and a good example of the truth of the 
dictum, which was by some thought odd when first made, namely, that 
Darwin had restored teleology to natural history, from which the study 
of morphology had dissevered it. 
