The remarkable fertilization of Pterostylis was first described by myself in the "Transactions of the New Zealand Institute" (vol v, p. 352 et seq.). The upper sepal and petals are connate into a hood, at the back of which the column is placed. The tip of the lip, which is extremely sensitive, hangs out of the entrance of the flower, thus forming a convenient landing-place for insects. When touched by an insect it springs up, carrving the insect with it, and thus enclosing it within the flower. The position then occupied by the lip is that shown in fig. 2 of the accompanying plate, and the insect is enclosed in the space between the lip and the column. The hood-like flower prevents any escape to the right or left of the lip, and as the lip remains closely appressed to the projecting wings of the upper part of the column as long as the insect is present, the only mode of escape is by crawling up the front of the column and passing between the wings (see fig. 4). In doing this, it is first smeared with viscid matter from the rostellum, which proiects at the back of the passage between the wings, and then drags away the pollinia, which can hardly fail to adhere to its sticky body. When visiting another flower it must pass over the stigma before escaping, and can hardly fail to leave some of the pollinia on its viscid surface. From the above it is clear that the fertilization of the flower depends entirely on the irritability of the lip. With the view of proving this, on one occasion I removed the lip from twelve flowers while young, so that insect visitors would not be compelled to crawl out of the flower by the passage between the wings of the column. When these flowers commenced to wither thev were examined, when it was found that they were not fertilized, and that not a single pollen-mass had been removed from the anther. I have also repeatedly placed minute insects on the lip, thus causing them to become entrapped, and in several instances I have seen these escape from the flower in the manner described above, bearing pollinia on their backs. The whole of the New Zealand species of Pterostylis are fertilized in the manner described above; and, according to the researches of the late Mr. Fitzgerald, it is also the manner employed in the Australian species.
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