It is a natural inquiry how so many plants belonging to various very distinct families first came to have the development of their flowers arrested, so as ultimately to become cleistogamic. That a passage from the one state to the other is far from difficult is shown by the many recorded cases of gradations between the two states on the same plant, in Viola, Oxalis, Biophytum, Campanula, etc. In the several species of Viola the various parts of the flowers have also been modified in very different degrees. Those plants which in their own country produce flowers of full or nearly full size, but never expand (as with Thelymitra), and yet set fruit, might easily be rendered cleistogamic. Lathyrus nissolia seems to be in an incipient transitional state, as does Drosera Anglica, the flowers of which are not perfectly closed. There is good evidence that flowers sometimes fail to expand and are somewhat reduced in size, owing to exposure to unfavourable conditions, but still retain their fertility unimpaired. Linnaeus observed in 1753 that the flowers on several plants brought from Spain and grown at Upsala did not show any corolla and yet produced seeds. Asa Gray has seen flowers on exotic plants in the Northern United States which never expanded and yet fruited. With certain English plants, which bear flowers during nearly the whole year, Mr. Bennett found that those produced during the winter season were fertilised in the bud; whilst with other species having fixed times for flowering, but “which had been tempted by a mild January to put forth a few wretched flowers,” no pollen was discharged from the anthers, and no seed was formed. The flowers of Lysimachia vulgaris if fully exposed to the sun expand properly, while those growing in shady ditches have smaller corollas which open only slightly; and these two forms graduate into one another in intermediate stations. Herr Bouche’s observations are of especial interest, for he shows that both temperature and the amount of light affect the size of the corolla; and he gives measurements proving that with some plants the corolla is diminished by the increasing cold and darkness of the changing season, whilst with others it is diminished by the increasing heat and light. (8/32. For the statement by Linnaeus see Mohl in ‘Botanische Zeitung’ 1863 page 327. Asa Gray ‘American Journal of Science’ 2nd series volume 39 1865 page 105. Bennett in ‘Nature’ November 1869 page 11. The Reverend G. Henslow also says ‘Gardener’s Chronicle’ 1877 page 271, also ‘Nature’ October 19, 1876 page 543, “that when the autumn draws on, and habitually in winter for such of our wild flowers as blossom at that season” the flowers are self-fertilised. On Lysimachia H. Muller ‘Nature’ September 1873 page 433. Bouche ‘Sitzungsbericht der Gesell. Naturforsch. Freunde’ October 1874 page 90.)