i893. HYBRIDITY IN PLANTS. 207 



states that the cultivated grape-vine is also occasionally pollinated 

 by honey-bees. 



As has already been pointed out, those flowers which are 

 unisexual — i.e., which have either pistil and no stamens, or stamens 

 and no pistil — must necessarily be cross-pollinated. Schulz, 

 however, states that in many of our trees which are normally uni- 

 sexual, hermaphrodite flowers do occasionally occur. Thus, in the 

 elder, hermaphrodite flowers or transitional forms between these and 

 unisexual are frequently to be found at the base of the male catkins. 

 Hermaphrodite flowers also occur in the birch, though less frequently, 

 very rarely in the hazel ; in the oak there are often ovaries at the 

 base of the male catkins, and rudiments of stamens in the female 

 flowers. The mode of fertilisation of the hazel is involved in great 

 obscurity, since scarcely a trace of the ovules can be found in the 

 female flowers at the time when the catkins are discharging their 

 pollen. In the ash, all kmds of condition may be met with, male, 

 female, and hermaphrodite flowers ; and either the same or different 

 kinds on the same tree. The ash is probably on the road to becoming 

 completely dioecious. 



Few phenomena in physiology, whether animal or vegetable, are 

 more puzzling than those of parthenogenesis, that is, the production of 

 a normal fertile embryo without any preceding act of fertilisation. 

 The example in the vegetable kingdom of Ccelebogyne is familiar to all 

 students of text-books. Another very remarkable instance is now on 

 record. There have been few more interesting contributions to 

 botanical science during the last few years than Dr. D. D. Cunning- 

 ham's "On the Phenomena of Fertilisation in Fiats Roxbiirghii," pub- 

 lished in Calcutta in i88g, with beautiful illustrations. According to 

 Dr. Cunningham the figs are in this species either male or female, 

 all on the same plant being of the same sex. The male figs contain 

 perfect male flowers, which produce pollen, and atrophied female or 

 " gall-flowers," which never produce seed, but within the ovaries of 

 which the eggs of an insect — usually a species of Eitpristis — are de- 

 posited and develop into pupae. The female figs contain perfect 

 female flowers, in which the eggs of the insect are never found, and 

 which produce fertile seeds. The terminal opening of both the male 

 and female figs is so obstructed by a covering of bracts that they are 

 almost completely closed chambers ; and the perfect development of 

 both the male and female flowers is dependent on the access of the 

 " fig-insect " to the interior of the cavity, without which they do not 

 arrive at a functional condition. Although the development of the 

 embryo in the female fig is essentially connected with the access of 

 the insects to the cavity, Dr. Cunningham believes that it does not 

 depend on the introduction of pollen by their agency. The nearly 

 entire closure of the opening by bracts presents an almost insuperable 

 obstacle to the introduction into the female fig of a sufficient quantity 

 of pollen for the fertilisation of every one of the very numerous ovules 



