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 

 (JDrosera 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 

 Dionsea, 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 Linnaean 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. 1 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 Dionsea. 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 Dionsea 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. 



