This section is from the book "The Gardener's Monthly And Horticulturist V26", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
"J.."Montgomery county, Pa., writes: "Enclosed are some specimens of clover heads, which you will find to have produced without flowers, just as the violet does, and which the scientific call cleistogene. I was not aware before that the clover could be ranked with this class. You will see, just as in other things of that class, that every flower produces a seed".
[Though some of these flowers exactly simulate cleistogene flowers, a careful examination showed that they had been attacked by the clover-seed fly, and this attack prevented the corollas from developing further than the mouth of the calyx, where they eventually died without fully expanding. There did appear to be two fully developed seeds in each little capsule, though still green, but in with them was the larva of the cecidomya, which had in some instances commenced to feed on the young seed, and would no doubt entirely devour them before they were wholly mature.
It opens up a field for an entirely new and interesting field for scientific observation. Dr. Engel-mann and Professor Riley a few years ago discovered that the Yucca moth fertilized the flowers of Yucca, - not for the purposes of cross-fertilization, as is supposed to be the special office of insects in these days of speculative science, - but with the flower's own pollen, and as it would seem to be with a sort of intuition that it was necessary to bring forward the seed towards maturity on which its young is to feed. So far as known there is no similar instance in the vegetable kingdom.
But we strongly suspect a similar case here. It is very doubtful whether the clover seed would have advanced so near perfection in its perfect condition without the agency of this little fly, - and this it has done without any relation to cross-fertilization, but in order that there may be food for its young! So far men of science will feel a very great interest in these clover heads, - but it is bad news for the clover-seed men that this foreign insect is getting such a strong hold here. Not even "humble-bees" will produce a crop of seeds where this little pest prevails.
It should be added that a large number proved on our examination not to have developed the young seed to the extent our correspondent's note supposes. The young germs seem to have been eaten away quite early, and the young larvae seemed to have nothing left to feed on but the remains of the imperfect corolla. - Ed. G. M].