As I was anxious to know whether this view was correct—­and as it seems a good illustration of how cautious we ought to be in assuming, as I had done with respect to the marginal spikes, that any fully developed structure is useless—­I applied to Dr. Canby.  He visited the native site of the plant, early in the season, before the leaves had grown to their full size, and sent me fourteen leaves, containing naturally captured insects.  Four of these had caught rather small insects, viz. three of them ants, and the fourth a rather small fly, but the other ten had all caught large insects, namely, five elaters, two chrysomelas, a curculio, a thick and broad spider, and a scolopendra.  Out of these ten insects, no less than eight [page 313] were beetles,* and out of the whole fourteen there was only one, viz. a dipterous insect, which could readily take flight.  Drosera, on the other hand, lives chiefly on insects which are good flyers, especially Diptera, caught by the aid of its viscid secretion.  But what most concerns us is the size of the ten larger insects.  Their average length from head to tail was .256 of an inch, the lobes of the leaves being on an average .53 of an inch in length, so that the insects were very nearly half as long as the leaves within which they were enclosed.  Only a few of these leaves, therefore, had wasted their powers by capturing small prey, though it is probable that many small insects had crawled over them and been caught, but had then escaped through the bars.

The Transmission of the Motor Impulse, and Means of Movement.—­It is sufficient to touch any one of the six filaments to cause both lobes to close, these becoming at the same time incurved throughout their whole breadth.  The stimulus must therefore radiate in all directions from any one filament.  It must also be transmitted with much rapidity across the leaf, for in all ordinary cases both lobes close simultaneously, as far as the eye can judge.  Most physiologists believe that in irritable plants the excitement is transmitted along, or in close connection with, the fibro-vascular bundles.  In Dionaea, the course of these vessels (composed of spiral and ordinary vascular

* Dr. Canby remarks (’Gardener’s Monthly,’ August 1868), “as a general thing beetles and insects of that kind, though always killed, seem to be too hard-shelled to serve as food, and after a short time are rejected.”  I am surprised at this statement, at least with respect to such beetles as elaters, for the five which I examined were in an extremely fragile and empty condition, as if all their internal parts had been partially digested.  Mrs. Treat informs me that the plants which she cultivated in New Jersey chiefly caught Diptera. [page 314]