THE FETJIT. 139 



bending over of the nucleus upon itself in the form of the letter U, 

 carrying the micropyle (b) over, but leaving the chalaza in its natural 

 vicinity to the hilum. There is no raphe in such ovules. 



Another condition more rarely met with is the horizontal or 

 amphitropous ovule, intermediate between straight and inverted, the 

 adherent funiculus pushing up the chalaza at one end, while the 

 micropyle descends in a corresponding degree, until the axis of the 

 ovule becomes horizontal, and parallel with instead of at right angles 

 to the placenta. 



In the first instance all ovules are straight, but they mostly become 

 curved during the course of their development. 



The Embryo-sac. At the time when the flower expands, there 

 exists a more or less considerable sac or cavity excavated in the 



substance of the nucleus, the upper end of which sac is situated 

 just within the apex. This cavity is called the embryo-sac, being 

 really a sac or bag with a proper wall, within which the embryo or 

 rudiment of the future plant is developed after fecundation. It is 

 analogous to the macrospore of Cryptogamous plants. 



The phenomena of fecundation and of the early development of the 

 embryo, together with the minutiae of the anatomy of ovules, are reserved 

 for the Physiological part of this work. 



The further morphological peculiarities of the ovular structures will 

 fall best under the head of the seed or completed product, previously to 

 examining which we must follow out the ultimate history of the pistils 

 and associated organs forming the fruit, in which the ripe seeds are 

 found. 



The Fruit. The fertilization of the ovules usually takes place 

 soon after the opening of the flowers, or sometimes even before 

 their expansion. During the subsequent changes by which the 

 ovules are converted into seeds, the ovary (and occasionally other 

 parts of the flower) undergoes further development, and becomes 

 what is technically called the fruit or seed-vessel. 



Changes during the ripening of the Fruit. Generally the stamens 

 and corolla, and not unfrequently the calyx also, fall away or wither up 

 after fertilization, and the styles, with the stigmas, mostly disappear ; but 

 the style sometimes persists, and even undergoes enlargement, forming a 

 kind of beak or tail to the fruit, especially in simple fruits formed of one 

 carpel (Ranunculus, Clematis, Geum, fig. 289, &c.). The calyx, when 

 inferior, remains in many cases as a loose cup or envelope surrounding 

 the fruit (as in Labiatse, many Solauacese, fig. 184, &c.) ; or, when superior, 

 its segments, enlarged or withered, form a kind of crown to the fruit (Com- 

 positee, Canipanulacea3, &c., fig. 283), and the tubes of adherent calyces 

 always enter into the composition of the inferior fruits (figs. 298-303). 

 In some cases the calyx and the corolla, in other cases the receptacle, 



