It has been observed by Professor E. Morren that doubleness of the flowers and variegation of the leaves are antagonistic states; but so many exceptions to the rule have lately been recorded (18/100. 'Gardener's Chronicle' 1865 page 626; 1866 pages 290, 730; and Verlot 'Des Varietes' page 75.), that, though general, it cannot be looked at as invariable. Variegation seems generally to result from a feeble or atrophied condition of the plant, and a large proportion of the seedlings raised from parents, if both are variegated, usually perish at an early age; hence we may perhaps infer that doubleness, which is the antagonistic state, commonly arises from a plethoric condition. On the other hand, extremely poor soil sometimes, though rarely, appears to cause doubleness: I formerly described (18/101. 'Gardener's Chronicle' 1843 page 628. In this article I suggested the theory above given on the doubleness of flowers. This view is adopted by Carriere 'Production et Fix. des Varietes' 1865 page 67.) some completely double, bud-like, flowers produced in large numbers by stunted wild plants of Gentiana amarella growing on a poor chalky bank. I have also noticed a distinct tendency to doubleness in the flowers of a Ranunculus, Horse-chestnut, and Bladder-nut (Ranunculus repens, Aesculus pavia, and Staphylea), growing under very unfavourable conditions. Professor Lehmann (18/102. Quoted by Gartner 'Bastarderzeugung' s. 567.) found several wild plants growing near a hot spring with double flowers. With respect to the cause of doubleness, which arises, as we see, under widely different circumstances, I shall presently attempt to show that the most probable view is that unnatural conditions first give a tendency to sterility, and that then, on the principle of compensation, as the reproductive organs do not perform their proper functions, they either become developed into petals, or additional petals are formed. This view has lately been supported by Mr. Laxton (18/103. 'Gardener's Chronicle' 1866 page 901.) who advances the case of some common peas, which, after long-continued heavy rain, flowered a second time, and produced double flowers.
SEEDLESS FRUIT.
Many of our most valuable fruits, although consisting in a homological sense of widely different organs, are either quite sterile, or produce extremely few seeds. This is notoriously the case with our best pears, grapes, and figs, with the pine-apple, banana, bread-fruit, pomegranate, azarole, date-palms, and some members of the orange-tribe. Poorer varieties of these same fruits either habitually or occasionally yield seed. (18/104. Lindley 'Theory of Horticulture' pages 175-179; Godron 'De l'Espece' tome 2 page 106; Pickering 'Races of Man;' Gallesio 'Teoria della Riproduzione' l816 pages 101-110. Meyen 'Reise um Erde' Th. 2 s. 214 states that at Manilla one variety of the banana is full of seeds: and Chamisso (Hooker's 'Bot. Misc.' volume 1 page 310) describes a variety of the bread-fruit in the Mariana Islands with small fruit, containing seeds which are frequently perfect. Burnes in his 'Travels in Bokhara' remarks on the pomegranate seeding in Mazenderan, as a remarkable peculiarity.) Most horticulturists look at the great size and anomalous development of the fruit as the cause, and sterility as the result; but the opposite view, as we shall presently see, is more probable.
STERILITY FROM THE EXCESSIVE DEVELOPMENT OF THE ORGANS OF GROWTH OR VEGETATION.
Plants which from any cause grow too luxuriantly, and produce leaves, stems, runners, suckers, tubers, bulbs, etc., in excess, sometimes do not flower, or if they flower do not yield seed. To make European vegetables under the hot climate of India yield seed, it is necessary to check their growth; and, when one-third grown, they are taken up, and their stems and tap-roots are cut or mutilated. (18/105. Ingledew in 'Transact. of Agricult. and Hort. Soc. of India' volume 2.) So it is with hybrids; for instance, Prof. Lecoq (18/106. 'De la Fecondation' 1862 page 308.) had three plants of Mirabilis, which, though they grew luxuriantly and flowered, were quite sterile; but after beating one with a stick until a few branches alone were left, these at once yielded good seed.