When in this state they exactly resemble the anthers of the most sterile hybrids. Gartner (18/88. 'Beitrage zur Kenntniss' etc. s. 117 et seq.; Kolreuter 'Zweite Fortsetzung' s. 10, 121; 'Dritte Fortsetzung' s. 57. Herbert 'Amaryllidaceae' page 355. Wiegmann 'Ueber die Bastarderzeugung' s. 27.), in his discussion on this subject, has shown that plants of many orders are occasionally thus affected; but the Caryophyllaceae and Liliaceae suffer most, and to these orders, I think, the Ericaceae may be added. Contabescence varies in degree, but on the same plant all the flowers are generally affected to nearly the same extent. The anthers are affected at a very early period in the flower-bud, and remain in the same state (with one recorded exception) during the life of the plant. The affection cannot be cured by any change of treatment, and is propagated by layers, cuttings, etc., and perhaps even by seed. In contabescent plants the female organs are seldom affected, or merely become precocious in their development. The cause of this affection is doubtful, and is different in different cases. Until I read Gartner's discussion I attributed it, as apparently did Herbert, to the unnatural treatment of the plants; but its permanence under changed conditions, and the female organs not being affected, seem incompatible with this view. The fact of several endemic plants becoming contabescent in our gardens seems, at first sight, equally incompatible with this view; but Kolreuter believes that this is the result of their transplantation. The contabescent plants of Dianthus and Verbascum, found wild by Wiegmann, grew on a dry and sterile bank. The fact that exotic plants are eminently liable to this affection also seems to show that it is in some manner caused by their unnatural treatment. In some instances, as with Silene, Gartner's view seems the most probable, namely, that it is caused by an inherent tendency in the species to become dioecious. I can add another cause, namely, the illegitimate unions of heterostyled plants, for I have observed seedlings of three species of Primula and of Lythrum salicaria, which had been raised from plants illegitimately fertilised by their own-form pollen, with some or all their anthers in a contabescent state. There is perhaps an additional cause, namely, self-fertilisation; for many plants of Dianthus and Lobelia, which had been raised from self-fertilised seeds, had their anthers in this state; but these instances are not conclusive, as both genera are liable from other causes to this affection.
Cases of an opposite nature likewise occur, namely, plants with the female organs struck with sterility, whilst the male organs remain perfect. Dianthus japonicus, a Passiflora, and Nicotiana, have been described by Gartner (18/89. 'Bastarderzengung' s. 356.) as being in this unusual condition.
MONSTROSITIES AS A CAUSE OF STERILITY.
Great deviations of structure, even when the reproductive organs themselves are not seriously affected, sometimes cause plants to become sterile. But in other cases plants may become monstrous to an extreme degree and yet retain their full fertility. Gallesio, who certainly had great experience (18/90. 'Teoria della Riproduzione' 1816 page 84; 'Traite du Citrus' 1811 page 67.), often attributes sterility to this cause; but it may be suspected that in some of his cases sterility was the cause, and not the result, of the monstrous growths. The curious St. Valery apple, although it bears fruit, rarely produces seed. The wonderfully anomalous flowers of Begonia frigida, formerly described, though they appear fit for fructification, are sterile. (18/91. Mr. C.W. Crocker in 'Gardener's Chronicle' 1861 page 1092.) Species of Primula in which the calyx is brightly coloured are said (18/92. Verlot 'Des Varietes' 1865 page 80.) to be often sterile, though I have known them to be fertile. On the other hand, Verlot gives several cases of proliferous flowers which can be propagated by seed. This was the case with a poppy, which had become monopetalous by the union of its petals.